diff --git a/CODING_STANDARDS.md b/CODING_STANDARDS.md
index c07b37b..30a3c27 100644
--- a/CODING_STANDARDS.md
+++ b/CODING_STANDARDS.md
@@ -94,3 +94,7 @@ These rules apply to every file in this repo , for humans and agents alike.
 4. **Needless complexity**.
 5. **Needless repetition**.
 6. **Opacity** — the code is hard to understand.
+
+## Credits
+
+Thanks to [@wojtekluwojteklu/clean_code.md](https://gist.github.com/wojteklu/73c6914cc446146b8b533c0988cf8d29)
diff --git a/README.md b/README.md
index c2e713a..7fd8294 100644
--- a/README.md
+++ b/README.md
@@ -17,7 +17,7 @@ Data is stored in `./data/` by default. For a real server (systemd, HTTPS, backu
 
 ### Develop
 
-Requires Go 1.25+, Node.js 22, [Bun](https://bun.sh) and [Task](https://taskfile.dev).
+Requires Go 1.27+, Node.js 22, [Bun](https://bun.sh) and [Task](https://taskfile.dev).
 
 ```sh
 cp .env.example .env
diff --git a/Taskfile.yml b/Taskfile.yml
index d9f56e6..b917c24 100644
--- a/Taskfile.yml
+++ b/Taskfile.yml
@@ -57,7 +57,7 @@ tasks:
     desc: Gremlins mutation testing of the use cases → tmp/gremlins.json
     cmds:
       - mkdir -p tmp
-      - gremlins unleash --integration --tags nofrontend --output tmp/gremlins.json ./internal/infrastructure/useCases
+      - gremlins unleash --integration --tags nofrontend --coverpkg=./internal/infrastructure/useCases/... --timeout-coefficient 10 --output tmp/gremlins.json ./internal/infrastructure/useCases
 
   lint:
     desc: gofmt check, go vet, eslint (--fix) and vue-tsc
diff --git a/docs/development.md b/docs/development.md
index 4718f45..b2a7382 100644
--- a/docs/development.md
+++ b/docs/development.md
@@ -4,7 +4,7 @@
 
 | Tool                          | Version                    | Install                                                  |
 |-------------------------------|----------------------------|----------------------------------------------------------|
-| [Go](https://go.dev/dl/)      | 1.25+ (see `go.mod`)       |                                                          |
+| [Go](https://go.dev/dl/)      | 1.27+ (see `go.mod`)       |                                                          |
 | [Node.js](https://nodejs.org) | 20.19+ or 22.12+ (22 LTS recommended) | `nvm install 22` — Vite and vue-tsc run on Node |
 | [Bun](https://bun.sh) (package manager and script runner) | 1.x | `powershell -c "irm bun.sh/install.ps1 \| iex"` or `curl -fsSL https://bun.sh/install \| bash` |
 | [Task](https://taskfile.dev)  | 3.43+                      | `go install github.com/go-task/task/v3/cmd/task@latest`  |
diff --git a/features/use_case_baseline.feature b/features/use_case_baseline.feature
new file mode 100644
index 0000000..883e286
--- /dev/null
+++ b/features/use_case_baseline.feature
@@ -0,0 +1,208 @@
+Feature: Use case baseline characterization
+
+  As the maintainer of RenewCMS
+  I want every use case in internal/infrastructure/useCases pinned down by tests
+  So that a refactor cannot silently change behaviour that callers already depend on
+
+  Background:
+    Given the article, image, user and mail repository fakes in test/ each implement their domain Repository interface in full, with no stubbed method returning a hardcoded zero value
+    And each fake mirrors the observable behaviour of the matching real repository in internal/infrastructure/persistence/repositories or internal/infrastructure/mailer, including which operations return a not-found style error for an unknown id and which succeed silently instead
+    And each fake can be configured to fail on its next call to a chosen method, independently of the state it already holds, returning a generic repository error
+
+  Scenario Outline: CreateArticle enforces the 3-200 character title length limit
+    Given an empty article repository fake
+    When CreateArticle is called with a title that is <length> characters long and a body "Some body text"
+    Then the result is <outcome>
+
+    Examples:
+      | length | outcome                                                                    |
+      | 0      | the error article.ErrInvalidTitle, and no article is stored               |
+      | 2      | the error article.ErrInvalidTitle, and no article is stored               |
+      | 3      | a created article whose id is repository-assigned and is_online is false  |
+      | 200    | a created article whose id is repository-assigned and is_online is false  |
+      | 201    | the error article.ErrInvalidTitle, and no article is stored               |
+
+  Scenario: CreateArticle propagates a configured repository failure
+    Given an article repository fake configured to fail on Create
+    When CreateArticle is called with a valid title "Backyard Renovation Update" and a body "Some body text"
+    Then the use case returns the repository's error unchanged
+    And no article is stored in the fake
+
+  Scenario Outline: GetArticle and GetOnlineArticle expose different behaviour for a missing article than for an offline one
+    Given an article repository fake containing:
+      | id | title           | is_online |
+      | 1  | Online Article  | true      |
+      | 2  | Offline Article | false     |
+    When <method> is called with id <id>
+    Then the result is <outcome>
+
+    Examples:
+      | method           | id | outcome                                                                                    |
+      | GetArticle       | 1  | the article with id 1                                                                      |
+      | GetArticle       | 2  | the article with id 2 (GetArticle does not hide offline articles)                          |
+      | GetArticle       | 9  | the repository's not-found error (gorm.ErrRecordNotFound)                                  |
+      | GetOnlineArticle | 1  | the article with id 1                                                                      |
+      | GetOnlineArticle | 2  | the error article.ErrArticleNotFound                                                       |
+      | GetOnlineArticle | 9  | the repository's not-found error (gorm.ErrRecordNotFound), not article.ErrArticleNotFound  |
+
+  Scenario Outline: GetArticleByName delegates verbatim to the repository
+    Given an article repository fake containing an article titled "Backyard Renovation Update" with id 1
+    When GetArticleByName is called with "<name>"
+    Then the result is <outcome>
+
+    Examples:
+      | name                       | outcome                                                    |
+      | Backyard Renovation Update | the article with id 1                                      |
+      | Unknown Title              | the repository's not-found error (gorm.ErrRecordNotFound)  |
+
+  Scenario Outline: ListArticles filters by is_online
+    Given an article repository fake containing:
+      | id | title | is_online |
+      | 1  | A     | true      |
+      | 2  | B     | false     |
+      | 3  | C     | true      |
+    When <method> is called
+    Then the result is the articles with ids <ids>, and no error
+
+    Examples:
+      | method             | ids   |
+      | ListOnlineArticles | 1,3   |
+      | ListAllArticles    | 1,2,3 |
+
+  Scenario: Listing articles on an empty repository returns an empty slice, not an error
+    Given an empty article repository fake
+    When ListOnlineArticles is called
+    Then the result is an empty slice and no error
+
+  Scenario Outline: UpdateArticle delegates each operation to the repository and surfaces not-found for an unknown id
+    Given an article repository fake containing an article with id 1 and an image with id 1
+    When <method> is called with <input>
+    Then the result is <outcome>
+
+    Examples:
+      | method         | input                  | outcome                                                    |
+      | UpdateBody     | id 1, body "New body"  | the article with id 1 and body "New body"                  |
+      | UpdateBody     | id 9, body "New body"  | the repository's not-found error (gorm.ErrRecordNotFound)  |
+      | UpdateIsOnline | id 1, isOnline true    | the article with id 1 and is_online true                   |
+      | UpdateIsOnline | id 9, isOnline true    | the repository's not-found error (gorm.ErrRecordNotFound)  |
+      | AddImage       | articleId 1, imageId 1 | no error, and the image is attached to the article         |
+      | AddImage       | articleId 9, imageId 1 | the repository's not-found error (gorm.ErrRecordNotFound)  |
+      | AddImage       | articleId 1, imageId 9 | the repository's not-found error (gorm.ErrRecordNotFound)  |
+
+  Scenario Outline: DeleteArticle succeeds silently whether or not the id exists
+    Given an article repository fake containing an article with id 1
+    When DeleteArticle is called with id <id>
+    Then no error is returned
+
+    Examples:
+      | id |
+      | 1  |
+      | 9  |
+
+  Scenario: DeleteArticle propagates a configured repository failure
+    Given an article repository fake configured to fail on Delete
+    When DeleteArticle is called with id 1
+    Then the use case returns the repository's error unchanged
+
+  Scenario Outline: CreateImage delegates verbatim to the repository, including its content-type check
+    Given an empty image repository fake that mirrors the real repository's accepted content types image/png, image/jpeg, image/webp and image/svg+xml
+    When CreateImage is called with content-type "<content_type>"
+    Then the result is <outcome>
+
+    Examples:
+      | content_type  | outcome                                                   |
+      | image/png     | a created image whose id is repository-assigned           |
+      | image/jpeg    | a created image whose id is repository-assigned           |
+      | image/webp    | a created image whose id is repository-assigned           |
+      | image/svg+xml | a created image whose id is repository-assigned           |
+      | image/gif     | an unsupported-content-type error, and no image is stored |
+
+  Scenario: CreateImage propagates a configured repository failure
+    Given an image repository fake configured to fail on Create
+    When CreateImage is called with a valid image/png input
+    Then the use case returns the repository's error unchanged
+
+  Scenario Outline: DeleteImage requires the image to exist, unlike article and user deletion
+    Given an image repository fake containing an image with id 1
+    When DeleteImage is called with id <id>
+    Then the result is <outcome>
+
+    Examples:
+      | id | outcome                                                    |
+      | 1  | no error, and the image is removed from the fake           |
+      | 9  | the repository's not-found error (gorm.ErrRecordNotFound)  |
+
+  Scenario: CreateUser assigns a fresh verification code and starts unverified
+    Given an empty user repository fake
+    When CreateUser is called with username "alice", password "hunter2example" and email "alice@example.com"
+    Then the result is a created user whose id is repository-assigned, is_verified is false, verification_code is a newly generated value distinct from any previous call, verification_expiration is about 2 hours from now, and password_reset_code is empty
+
+  Scenario: CreateUser propagates a configured repository failure
+    Given a user repository fake configured to fail on Create
+    When CreateUser is called with a valid username, password and email
+    Then the use case returns the repository's error unchanged
+
+  Scenario Outline: GetUser reads by id, username or email and surfaces not-found
+    Given a user repository fake containing a user with id 1, username "alice" and email "alice@example.com"
+    When <method> is called with "<input>"
+    Then the result is <outcome>
+
+    Examples:
+      | method            | input             | outcome                                                    |
+      | GetUser           | 1                 | the user with id 1                                         |
+      | GetUser           | 9                 | the repository's not-found error (gorm.ErrRecordNotFound)  |
+      | GetUserByUsername | alice             | the user with id 1                                         |
+      | GetUserByUsername | bob               | the repository's not-found error (gorm.ErrRecordNotFound)  |
+      | GetUserByEmail    | alice@example.com | the user with id 1                                         |
+      | GetUserByEmail    | bob@example.com   | the repository's not-found error (gorm.ErrRecordNotFound)  |
+
+  Scenario: ListUsers returns every user in the fake
+    Given a user repository fake containing users with ids 1 and 2
+    When ListUsers is called
+    Then the result is the users with ids 1 and 2, and no error
+
+  Scenario Outline: UpdateUser delegates each operation to the repository and surfaces not-found for an unknown id
+    Given a user repository fake containing a user with id 1
+    When <method> is called with id <id> and <input>
+    Then the result is <outcome>
+
+    Examples:
+      | method                   | id | input                     | outcome                                                    |
+      | UpdateVerificationStatus | 1  | isVerified true           | the user with id 1 and is_verified true                    |
+      | UpdateVerificationStatus | 9  | isVerified true           | the repository's not-found error (gorm.ErrRecordNotFound)  |
+      | UpdatePassword           | 1  | password "newpassword123" | the user with id 1                                         |
+      | UpdatePassword           | 9  | password "newpassword123" | the repository's not-found error (gorm.ErrRecordNotFound)  |
+      | UpdatePasswordResetCode  | 1  | code "reset-code-123"     | the user with id 1                                         |
+      | UpdatePasswordResetCode  | 9  | code "reset-code-123"     | the repository's not-found error (gorm.ErrRecordNotFound)  |
+
+  Scenario Outline: DeleteUser succeeds silently whether or not the id exists
+    Given a user repository fake containing a user with id 1
+    When DeleteUser is called with id <id>
+    Then no error is returned
+
+    Examples:
+      | id |
+      | 1  |
+      | 9  |
+
+  Scenario Outline: SendMail forwards its arguments verbatim to the mail repository
+    Given a mail repository fake
+    When SendMail is called with receiver "<receiver>", template "<template>" and some data
+    Then the fake recorded exactly one send with that receiver, template and data, and no error is returned
+
+    Examples:
+      | receiver          | template       |
+      | alice@example.com | verify-email   |
+      | bob@example.com   | password-reset |
+
+  Scenario: SendMail propagates a configured repository failure without recording a send
+    Given a mail repository fake configured to fail
+    When SendMail is called with receiver "carol@example.com", template "welcome" and nil data
+    Then the use case returns the repository's error unchanged
+    And the fake recorded no send
+
+  Scenario: Mutation testing runs clean on the use cases package
+    Given the test/ suite passes via `go test -tags nofrontend ./test/... -count=1`
+    When `gremlins unleash --integration --tags nofrontend --coverpkg=./internal/infrastructure/useCases/... --timeout-coefficient 10 --output tmp/gremlins.json ./internal/infrastructure/useCases` is run
+    Then the report contains zero mutants with status LIVED
+    And the report contains zero mutants with status NOT COVERED
diff --git a/go.mod b/go.mod
index 941a879..b41594a 100644
--- a/go.mod
+++ b/go.mod
@@ -1,10 +1,11 @@
 module RenewCMS
 
-go 1.25.4
+go 1.27.1
 
 require (
 	github.com/MadAppGang/httplog v1.3.0
 	github.com/glebarez/sqlite v1.11.0
+	github.com/go-chi/chi/v5 v5.2.3
 	github.com/go-chi/cors v1.2.2
 	github.com/go-chi/jwtauth/v5 v5.3.3
 	github.com/go-playground/validator/v10 v10.28.0
@@ -34,10 +35,13 @@ require (
 	github.com/lestrrat-go/iter v1.0.2 // indirect
 	github.com/lestrrat-go/jwx/v2 v2.1.6 // indirect
 	github.com/lestrrat-go/option v1.0.1 // indirect
+	github.com/mattn/go-colorable v0.1.14 // indirect
+	github.com/mattn/go-isatty v0.0.20 // indirect
 	github.com/ncruces/go-strftime v1.0.0 // indirect
 	github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec // indirect
 	github.com/segmentio/asm v1.2.1 // indirect
 	golang.org/x/exp v0.0.0-20251113190631-e25ba8c21ef6 // indirect
+	golang.org/x/sys v0.38.0 // indirect
 	golang.org/x/text v0.31.0 // indirect
 	gopkg.in/alexcesaro/quotedprintable.v3 v3.0.0-20150716171945-2caba252f4dc // indirect
 	modernc.org/libc v1.67.0 // indirect
@@ -45,10 +49,3 @@ require (
 	modernc.org/memory v1.11.0 // indirect
 	modernc.org/sqlite v1.40.1 // indirect
 )
-
-require (
-	github.com/go-chi/chi/v5 v5.2.3
-	github.com/mattn/go-colorable v0.1.14 // indirect
-	github.com/mattn/go-isatty v0.0.20 // indirect
-	golang.org/x/sys v0.38.0 // indirect
-)
diff --git a/test/article_test.go b/test/article_test.go
index 2827a0c..508336c 100644
--- a/test/article_test.go
+++ b/test/article_test.go
@@ -2,58 +2,150 @@ package test
 
 import (
 	"RenewCMS/internal/domain/article"
+	imageDomain "RenewCMS/internal/domain/image"
 	"RenewCMS/internal/infrastructure/useCases"
 	"errors"
+	"sort"
 	"testing"
+
+	"gorm.io/gorm"
 )
 
 type mockArticleRepo struct {
 	articles map[uint32]article.Article
+	images   map[uint32]*imageDomain.Image
+	nextID   uint32
+	fail     failSwitch
 }
 
-func (m *mockArticleRepo) FindByFilters(f article.Filters) ([]article.Article, error) {
-	var results []article.Article
-	for _, a := range m.articles {
-		if f.IsOnline != nil && a.IsOnline == *f.IsOnline {
-			results = append(results, a)
-		}
+func newMockArticleRepo() *mockArticleRepo {
+	return &mockArticleRepo{
+		articles: make(map[uint32]article.Article),
+		images:   make(map[uint32]*imageDomain.Image),
 	}
-	return results, nil
+}
+
+func (m *mockArticleRepo) sortedIds() []uint32 {
+	ids := make([]uint32, 0, len(m.articles))
+	for id := range m.articles {
+		ids = append(ids, id)
+	}
+	sort.Slice(ids, func(i, j int) bool { return ids[i] < ids[j] })
+	return ids
+}
+
+func (m *mockArticleRepo) FindByFilters(filters article.Filters) ([]article.Article, error) {
+	if err := m.fail.trigger("FindByFilters"); err != nil {
+		return nil, err
+	}
+	result := make([]article.Article, 0)
+	for _, id := range m.sortedIds() {
+		a := m.articles[id]
+		if filters.IsOnline != nil && a.IsOnline != *filters.IsOnline {
+			continue
+		}
+		result = append(result, a)
+	}
+	return result, nil
 }
 
 func (m *mockArticleRepo) Get(id uint32) (article.Article, error) {
+	if err := m.fail.trigger("Get"); err != nil {
+		return article.Article{}, err
+	}
 	a, ok := m.articles[id]
 	if !ok {
-		return article.Article{}, article.ErrArticleNotFound
+		return article.Article{}, gorm.ErrRecordNotFound
 	}
 	return a, nil
 }
 
+func (m *mockArticleRepo) GetByName(name string) (article.Article, error) {
+	if err := m.fail.trigger("GetByName"); err != nil {
+		return article.Article{}, err
+	}
+	for _, id := range m.sortedIds() {
+		a := m.articles[id]
+		if a.Title == name {
+			return a, nil
+		}
+	}
+	return article.Article{}, gorm.ErrRecordNotFound
+}
+
+func (m *mockArticleRepo) GetAll() []article.Article {
+	result := make([]article.Article, 0)
+	for _, id := range m.sortedIds() {
+		result = append(result, m.articles[id])
+	}
+	return result
+}
+
 func (m *mockArticleRepo) Create(a article.Article) (article.Article, error) {
-	a.ID = uint32(len(m.articles) + 1)
+	if err := m.fail.trigger("Create"); err != nil {
+		return article.Article{}, err
+	}
+	m.nextID++
+	a.ID = m.nextID
 	m.articles[a.ID] = a
 	return a, nil
 }
 
+func (m *mockArticleRepo) UpdateBody(id uint32, body string) (article.Article, error) {
+	if err := m.fail.trigger("UpdateBody"); err != nil {
+		return article.Article{}, err
+	}
+	a, ok := m.articles[id]
+	if !ok {
+		return article.Article{}, gorm.ErrRecordNotFound
+	}
+	a.Body = body
+	m.articles[id] = a
+	return a, nil
+}
+
+func (m *mockArticleRepo) UpdateIsOnline(id uint32, isOnline bool) (article.Article, error) {
+	if err := m.fail.trigger("UpdateIsOnline"); err != nil {
+		return article.Article{}, err
+	}
+	a, ok := m.articles[id]
+	if !ok {
+		return article.Article{}, gorm.ErrRecordNotFound
+	}
+	a.IsOnline = isOnline
+	m.articles[id] = a
+	return a, nil
+}
+
 func (m *mockArticleRepo) Delete(id uint32) error {
+	if err := m.fail.trigger("Delete"); err != nil {
+		return err
+	}
 	delete(m.articles, id)
 	return nil
 }
 
-func (m *mockArticleRepo) GetByName(n string) (article.Article, error) { return article.Article{}, nil }
-func (m *mockArticleRepo) GetAll() []article.Article                   { return nil }
-func (m *mockArticleRepo) UpdateBody(id uint32, b string) (article.Article, error) {
-	return article.Article{}, nil
+func (m *mockArticleRepo) AddImage(articleId uint32, imageId uint32) error {
+	if err := m.fail.trigger("AddImage"); err != nil {
+		return err
+	}
+	a, ok := m.articles[articleId]
+	if !ok {
+		return gorm.ErrRecordNotFound
+	}
+	img, ok := m.images[imageId]
+	if !ok {
+		return gorm.ErrRecordNotFound
+	}
+	a.Images = append(a.Images, img)
+	m.articles[articleId] = a
+	return nil
 }
-func (m *mockArticleRepo) UpdateIsOnline(id uint32, o bool) (article.Article, error) {
-	return article.Article{}, nil
-}
-func (m *mockArticleRepo) AddImage(p, i uint32) error { return nil }
 
 var _ article.Repository = &mockArticleRepo{}
 
 func TestCreateArticle(t *testing.T) {
-	repo := &mockArticleRepo{articles: make(map[uint32]article.Article)}
+	repo := newMockArticleRepo()
 	uc := useCases.NewCreateArticleUseCase(repo)
 
 	t.Run("Valid Title", func(t *testing.T) {
@@ -77,10 +169,9 @@ func TestCreateArticle(t *testing.T) {
 }
 
 func TestGetOnlineArticle(t *testing.T) {
-	repo := &mockArticleRepo{articles: map[uint32]article.Article{
-		1: {ID: 1, IsOnline: true},
-		2: {ID: 2, IsOnline: false},
-	}}
+	repo := newMockArticleRepo()
+	repo.articles[1] = article.Article{ID: 1, IsOnline: true}
+	repo.articles[2] = article.Article{ID: 2, IsOnline: false}
 	uc := useCases.NewGetArticleUseCase(repo)
 
 	t.Run("Article Online", func(t *testing.T) {
diff --git a/test/fakes_common.go b/test/fakes_common.go
new file mode 100644
index 0000000..12a6651
--- /dev/null
+++ b/test/fakes_common.go
@@ -0,0 +1,21 @@
+package test
+
+import "errors"
+
+var errRepositoryFailure = errors.New("repository failure")
+
+type failSwitch struct {
+	method string
+}
+
+func (f *failSwitch) failNext(method string) {
+	f.method = method
+}
+
+func (f *failSwitch) trigger(method string) error {
+	if f.method == method {
+		f.method = ""
+		return errRepositoryFailure
+	}
+	return nil
+}
diff --git a/test/image_test.go b/test/image_test.go
index 2e1097a..f51779c 100644
--- a/test/image_test.go
+++ b/test/image_test.go
@@ -1,40 +1,71 @@
 package test
 
 import (
-	"RenewCMS/internal/domain/image"
+	imageDomain "RenewCMS/internal/domain/image"
 	"RenewCMS/internal/infrastructure/useCases"
+	"errors"
+	"io"
 	"strings"
 	"testing"
+
+	"gorm.io/gorm"
 )
 
-type mockImageRepo struct {
-	images map[uint32]image.Image
+var errUnsupportedImageContentType = errors.New("the file must be a PNG, JPEG, WEBP, or SVG image")
+
+var supportedImageContentTypes = map[string]bool{
+	"image/png":     true,
+	"image/jpeg":    true,
+	"image/webp":    true,
+	"image/svg+xml": true,
 }
 
-func (m *mockImageRepo) Create(input image.ImageInput) (image.Image, error) {
-	newId := uint32(len(m.images) + 1)
-	img := image.Image{
-		ID:   newId,
-		Path: "/static/" + input.Filename,
+type mockImageRepo struct {
+	images map[uint32]imageDomain.Image
+	nextID uint32
+	fail   failSwitch
+}
+
+func newMockImageRepo() *mockImageRepo {
+	return &mockImageRepo{images: make(map[uint32]imageDomain.Image)}
+}
+
+func (m *mockImageRepo) Create(input imageDomain.ImageInput) (imageDomain.Image, error) {
+	if err := m.fail.trigger("Create"); err != nil {
+		return imageDomain.Image{}, err
 	}
-	m.images[newId] = img
+	if !supportedImageContentTypes[input.ContentType] {
+		return imageDomain.Image{}, errUnsupportedImageContentType
+	}
+	if input.Content != nil {
+		_, _ = io.ReadAll(input.Content)
+	}
+	m.nextID++
+	img := imageDomain.Image{ID: m.nextID, Path: "/static/uploadedImages/" + input.Filename}
+	m.images[img.ID] = img
 	return img, nil
 }
 
 func (m *mockImageRepo) Delete(id uint32) error {
+	if err := m.fail.trigger("Delete"); err != nil {
+		return err
+	}
+	if _, ok := m.images[id]; !ok {
+		return gorm.ErrRecordNotFound
+	}
 	delete(m.images, id)
 	return nil
 }
 
-var _ image.Repository = &mockImageRepo{}
+var _ imageDomain.Repository = &mockImageRepo{}
 
 func TestImageUseCases(t *testing.T) {
-	repo := &mockImageRepo{images: make(map[uint32]image.Image)}
+	repo := newMockImageRepo()
 	createUc := useCases.NewCreateImageUseCase(repo)
 	deleteUc := useCases.NewDeleteImageUseCase(repo)
 
 	t.Run("Create Image", func(t *testing.T) {
-		input := image.ImageInput{
+		input := imageDomain.ImageInput{
 			Content:     strings.NewReader("fake-image-data"),
 			Filename:    "test.png",
 			ContentType: "image/png",
@@ -53,7 +84,7 @@ func TestImageUseCases(t *testing.T) {
 	})
 
 	t.Run("Delete Image", func(t *testing.T) {
-		repo.images[99] = image.Image{ID: 99, Path: "/static/delete-me.png"}
+		repo.images[99] = imageDomain.Image{ID: 99, Path: "/static/delete-me.png"}
 
 		err := deleteUc.DeleteImage(99)
 		if err != nil {
diff --git a/test/mail_test.go b/test/mail_test.go
index b0b36aa..cd40730 100644
--- a/test/mail_test.go
+++ b/test/mail_test.go
@@ -7,35 +7,36 @@ import (
 	"testing"
 )
 
+type recordedMail struct {
+	Address  string
+	Template string
+	Data     any
+}
+
 type mockMailRepo struct {
-	SentEmails []struct {
-		Address  string
-		Template string
-		Data     any
-	}
-	ShouldFail bool
+	SentEmails []recordedMail
+	fail       failSwitch
+}
+
+func newMockMailRepo() *mockMailRepo {
+	return &mockMailRepo{}
 }
 
 func (m *mockMailRepo) Send(receiverAddress string, templateName string, data any) error {
-	if m.ShouldFail {
-		return errors.New("smtp error")
+	if err := m.fail.trigger("Send"); err != nil {
+		return err
 	}
-	m.SentEmails = append(m.SentEmails, struct {
-		Address  string
-		Template string
-		Data     any
-	}{receiverAddress, templateName, data})
+	m.SentEmails = append(m.SentEmails, recordedMail{receiverAddress, templateName, data})
 	return nil
 }
 
 var _ mail.Repository = &mockMailRepo{}
 
 func TestSendMail(t *testing.T) {
-	repo := &mockMailRepo{}
+	repo := newMockMailRepo()
 	uc := useCases.NewSendMailUseCase(repo)
 
 	t.Run("Successful Email Send", func(t *testing.T) {
-		repo.ShouldFail = false
 		err := uc.SendMail("user@example.com", "welcome", "User123")
 		if err != nil {
 			t.Fatalf("Expected no error, got %v", err)
@@ -46,10 +47,10 @@ func TestSendMail(t *testing.T) {
 	})
 
 	t.Run("Failed Email Send", func(t *testing.T) {
-		repo.ShouldFail = true
+		repo.fail.failNext("Send")
 		err := uc.SendMail("fail@example.com", "reset", nil)
-		if err == nil {
-			t.Errorf("Expected an error but got nil")
+		if !errors.Is(err, errRepositoryFailure) {
+			t.Errorf("Expected repository failure, got %v", err)
 		}
 	})
 }
diff --git a/test/use_case_baseline_test.go b/test/use_case_baseline_test.go
new file mode 100644
index 0000000..22a5a45
--- /dev/null
+++ b/test/use_case_baseline_test.go
@@ -0,0 +1,720 @@
+package test
+
+import (
+	"RenewCMS/internal/domain/article"
+	imageDomain "RenewCMS/internal/domain/image"
+	"RenewCMS/internal/domain/user"
+	"RenewCMS/internal/infrastructure/useCases"
+	"errors"
+	"fmt"
+	"reflect"
+	"strings"
+	"testing"
+	"time"
+
+	"gorm.io/gorm"
+)
+
+func TestCreateArticleTitleLengthLimit(t *testing.T) {
+	cases := []struct {
+		length      int
+		expectValid bool
+	}{
+		{0, false},
+		{2, false},
+		{3, true},
+		{200, true},
+		{201, false},
+	}
+
+	for _, tc := range cases {
+		t.Run(fmt.Sprintf("length_%d", tc.length), func(t *testing.T) {
+			repo := newMockArticleRepo()
+			uc := useCases.NewCreateArticleUseCase(repo)
+
+			title := strings.Repeat("a", tc.length)
+			result, err := uc.CreateArticle(useCases.CreateArticleCommand{Title: title, Body: "Some body text"})
+
+			if tc.expectValid {
+				if err != nil {
+					t.Fatalf("expected no error, got %v", err)
+				}
+				if result.ID == 0 {
+					t.Errorf("expected repository-assigned id, got 0")
+				}
+				if result.IsOnline {
+					t.Errorf("expected is_online false, got true")
+				}
+				if len(repo.articles) != 1 {
+					t.Errorf("expected 1 article stored, got %d", len(repo.articles))
+				}
+			} else {
+				if !errors.Is(err, article.ErrInvalidTitle) {
+					t.Errorf("expected article.ErrInvalidTitle, got %v", err)
+				}
+				if len(repo.articles) != 0 {
+					t.Errorf("expected no article stored, got %d", len(repo.articles))
+				}
+			}
+		})
+	}
+}
+
+func TestCreateArticlePropagatesRepositoryFailure(t *testing.T) {
+	repo := newMockArticleRepo()
+	repo.fail.failNext("Create")
+	uc := useCases.NewCreateArticleUseCase(repo)
+
+	_, err := uc.CreateArticle(useCases.CreateArticleCommand{Title: "Backyard Renovation Update", Body: "Some body text"})
+
+	if !errors.Is(err, errRepositoryFailure) {
+		t.Errorf("expected repository failure, got %v", err)
+	}
+	if len(repo.articles) != 0 {
+		t.Errorf("expected no article stored, got %d", len(repo.articles))
+	}
+}
+
+func TestGetArticleAndGetOnlineArticle(t *testing.T) {
+	newRepo := func() *mockArticleRepo {
+		repo := newMockArticleRepo()
+		repo.articles[1] = article.Article{ID: 1, Title: "Online Article", IsOnline: true}
+		repo.articles[2] = article.Article{ID: 2, Title: "Offline Article", IsOnline: false}
+		return repo
+	}
+
+	t.Run("GetArticle_1", func(t *testing.T) {
+		repo := newRepo()
+		uc := useCases.NewGetArticleUseCase(repo)
+		result, err := uc.GetArticle(1)
+		if err != nil {
+			t.Fatalf("expected no error, got %v", err)
+		}
+		if result.ID != 1 {
+			t.Errorf("expected article id 1, got %d", result.ID)
+		}
+	})
+
+	t.Run("GetArticle_2", func(t *testing.T) {
+		repo := newRepo()
+		uc := useCases.NewGetArticleUseCase(repo)
+		result, err := uc.GetArticle(2)
+		if err != nil {
+			t.Fatalf("expected no error, got %v", err)
+		}
+		if result.ID != 2 {
+			t.Errorf("expected article id 2, got %d", result.ID)
+		}
+	})
+
+	t.Run("GetArticle_9", func(t *testing.T) {
+		repo := newRepo()
+		uc := useCases.NewGetArticleUseCase(repo)
+		_, err := uc.GetArticle(9)
+		if !errors.Is(err, gorm.ErrRecordNotFound) {
+			t.Errorf("expected gorm.ErrRecordNotFound, got %v", err)
+		}
+	})
+
+	t.Run("GetOnlineArticle_1", func(t *testing.T) {
+		repo := newRepo()
+		uc := useCases.NewGetArticleUseCase(repo)
+		result, err := uc.GetOnlineArticle(1)
+		if err != nil {
+			t.Fatalf("expected no error, got %v", err)
+		}
+		if result.ID != 1 {
+			t.Errorf("expected article id 1, got %d", result.ID)
+		}
+	})
+
+	t.Run("GetOnlineArticle_2", func(t *testing.T) {
+		repo := newRepo()
+		uc := useCases.NewGetArticleUseCase(repo)
+		_, err := uc.GetOnlineArticle(2)
+		if !errors.Is(err, article.ErrArticleNotFound) {
+			t.Errorf("expected article.ErrArticleNotFound, got %v", err)
+		}
+	})
+
+	t.Run("GetOnlineArticle_9", func(t *testing.T) {
+		repo := newRepo()
+		uc := useCases.NewGetArticleUseCase(repo)
+		_, err := uc.GetOnlineArticle(9)
+		if !errors.Is(err, gorm.ErrRecordNotFound) {
+			t.Errorf("expected gorm.ErrRecordNotFound, got %v", err)
+		}
+		if errors.Is(err, article.ErrArticleNotFound) {
+			t.Errorf("expected the raw not-found error, not article.ErrArticleNotFound")
+		}
+	})
+}
+
+func TestGetArticleByNameDelegatesVerbatim(t *testing.T) {
+	newRepo := func() *mockArticleRepo {
+		repo := newMockArticleRepo()
+		repo.articles[1] = article.Article{ID: 1, Title: "Backyard Renovation Update"}
+		return repo
+	}
+
+	t.Run("Backyard_Renovation_Update", func(t *testing.T) {
+		repo := newRepo()
+		uc := useCases.NewGetArticleUseCase(repo)
+		result, err := uc.GetArticleByName("Backyard Renovation Update")
+		if err != nil {
+			t.Fatalf("expected no error, got %v", err)
+		}
+		if result.ID != 1 {
+			t.Errorf("expected article id 1, got %d", result.ID)
+		}
+	})
+
+	t.Run("Unknown_Title", func(t *testing.T) {
+		repo := newRepo()
+		uc := useCases.NewGetArticleUseCase(repo)
+		_, err := uc.GetArticleByName("Unknown Title")
+		if !errors.Is(err, gorm.ErrRecordNotFound) {
+			t.Errorf("expected gorm.ErrRecordNotFound, got %v", err)
+		}
+	})
+}
+
+func assertArticleIds(t *testing.T, articles []article.Article, expected []uint32) {
+	t.Helper()
+	if len(articles) != len(expected) {
+		t.Fatalf("expected %d articles, got %d", len(expected), len(articles))
+	}
+	for i, id := range expected {
+		if articles[i].ID != id {
+			t.Errorf("expected article id %d at index %d, got %d", id, i, articles[i].ID)
+		}
+	}
+}
+
+func TestListArticlesFiltersByIsOnline(t *testing.T) {
+	newRepo := func() *mockArticleRepo {
+		repo := newMockArticleRepo()
+		repo.articles[1] = article.Article{ID: 1, Title: "A", IsOnline: true}
+		repo.articles[2] = article.Article{ID: 2, Title: "B", IsOnline: false}
+		repo.articles[3] = article.Article{ID: 3, Title: "C", IsOnline: true}
+		return repo
+	}
+
+	t.Run("ListOnlineArticles", func(t *testing.T) {
+		repo := newRepo()
+		uc := useCases.NewListArticlesUseCase(repo)
+		result, err := uc.ListOnlineArticles()
+		if err != nil {
+			t.Fatalf("expected no error, got %v", err)
+		}
+		assertArticleIds(t, result, []uint32{1, 3})
+	})
+
+	t.Run("ListAllArticles", func(t *testing.T) {
+		repo := newRepo()
+		uc := useCases.NewListArticlesUseCase(repo)
+		result, err := uc.ListAllArticles()
+		if err != nil {
+			t.Fatalf("expected no error, got %v", err)
+		}
+		assertArticleIds(t, result, []uint32{1, 2, 3})
+	})
+}
+
+func TestListOnlineArticlesEmptyRepositoryReturnsEmptySlice(t *testing.T) {
+	repo := newMockArticleRepo()
+	uc := useCases.NewListArticlesUseCase(repo)
+
+	result, err := uc.ListOnlineArticles()
+	if err != nil {
+		t.Fatalf("expected no error, got %v", err)
+	}
+	if result == nil {
+		t.Errorf("expected an empty slice, got nil")
+	}
+	if len(result) != 0 {
+		t.Errorf("expected an empty slice, got %d items", len(result))
+	}
+}
+
+func TestUpdateArticleDelegatesEachOperation(t *testing.T) {
+	newRepo := func() *mockArticleRepo {
+		repo := newMockArticleRepo()
+		repo.articles[1] = article.Article{ID: 1, Title: "Existing"}
+		repo.images[1] = &imageDomain.Image{ID: 1, Path: "/static/one.png"}
+		return repo
+	}
+
+	t.Run("UpdateBody_id1", func(t *testing.T) {
+		repo := newRepo()
+		uc := useCases.NewUpdateArticleUseCase(repo)
+		result, err := uc.UpdateBody(1, "New body")
+		if err != nil {
+			t.Fatalf("expected no error, got %v", err)
+		}
+		if result.ID != 1 || result.Body != "New body" {
+			t.Errorf("unexpected result: %+v", result)
+		}
+	})
+
+	t.Run("UpdateBody_id9", func(t *testing.T) {
+		repo := newRepo()
+		uc := useCases.NewUpdateArticleUseCase(repo)
+		_, err := uc.UpdateBody(9, "New body")
+		if !errors.Is(err, gorm.ErrRecordNotFound) {
+			t.Errorf("expected gorm.ErrRecordNotFound, got %v", err)
+		}
+	})
+
+	t.Run("UpdateIsOnline_id1", func(t *testing.T) {
+		repo := newRepo()
+		uc := useCases.NewUpdateArticleUseCase(repo)
+		result, err := uc.UpdateIsOnline(1, true)
+		if err != nil {
+			t.Fatalf("expected no error, got %v", err)
+		}
+		if result.ID != 1 || !result.IsOnline {
+			t.Errorf("unexpected result: %+v", result)
+		}
+	})
+
+	t.Run("UpdateIsOnline_id9", func(t *testing.T) {
+		repo := newRepo()
+		uc := useCases.NewUpdateArticleUseCase(repo)
+		_, err := uc.UpdateIsOnline(9, true)
+		if !errors.Is(err, gorm.ErrRecordNotFound) {
+			t.Errorf("expected gorm.ErrRecordNotFound, got %v", err)
+		}
+	})
+
+	t.Run("AddImage_article1_image1", func(t *testing.T) {
+		repo := newRepo()
+		uc := useCases.NewUpdateArticleUseCase(repo)
+		err := uc.AddImage(1, 1)
+		if err != nil {
+			t.Fatalf("expected no error, got %v", err)
+		}
+		updated, err := repo.Get(1)
+		if err != nil {
+			t.Fatalf("expected no error, got %v", err)
+		}
+		if len(updated.Images) != 1 || updated.Images[0].ID != 1 {
+			t.Errorf("expected image 1 attached, got %+v", updated.Images)
+		}
+	})
+
+	t.Run("AddImage_article9_image1", func(t *testing.T) {
+		repo := newRepo()
+		uc := useCases.NewUpdateArticleUseCase(repo)
+		err := uc.AddImage(9, 1)
+		if !errors.Is(err, gorm.ErrRecordNotFound) {
+			t.Errorf("expected gorm.ErrRecordNotFound, got %v", err)
+		}
+	})
+
+	t.Run("AddImage_article1_image9", func(t *testing.T) {
+		repo := newRepo()
+		uc := useCases.NewUpdateArticleUseCase(repo)
+		err := uc.AddImage(1, 9)
+		if !errors.Is(err, gorm.ErrRecordNotFound) {
+			t.Errorf("expected gorm.ErrRecordNotFound, got %v", err)
+		}
+	})
+}
+
+func TestDeleteArticleSucceedsSilently(t *testing.T) {
+	for _, id := range []uint32{1, 9} {
+		t.Run(fmt.Sprintf("id_%d", id), func(t *testing.T) {
+			repo := newMockArticleRepo()
+			repo.articles[1] = article.Article{ID: 1}
+			uc := useCases.NewDeleteArticleUseCase(repo)
+
+			err := uc.DeleteArticle(id)
+			if err != nil {
+				t.Errorf("expected no error, got %v", err)
+			}
+		})
+	}
+}
+
+func TestDeleteArticlePropagatesRepositoryFailure(t *testing.T) {
+	repo := newMockArticleRepo()
+	repo.articles[1] = article.Article{ID: 1}
+	repo.fail.failNext("Delete")
+	uc := useCases.NewDeleteArticleUseCase(repo)
+
+	err := uc.DeleteArticle(1)
+	if !errors.Is(err, errRepositoryFailure) {
+		t.Errorf("expected repository failure, got %v", err)
+	}
+}
+
+func TestCreateImageDelegatesContentTypeCheck(t *testing.T) {
+	cases := []struct {
+		contentType string
+		valid       bool
+	}{
+		{"image/png", true},
+		{"image/jpeg", true},
+		{"image/webp", true},
+		{"image/svg+xml", true},
+		{"image/gif", false},
+	}
+
+	for _, tc := range cases {
+		t.Run(strings.ReplaceAll(tc.contentType, "/", "_"), func(t *testing.T) {
+			repo := newMockImageRepo()
+			uc := useCases.NewCreateImageUseCase(repo)
+
+			result, err := uc.CreateImage(imageDomain.ImageInput{
+				Content:     strings.NewReader("fake-image-data"),
+				Filename:    "test.img",
+				ContentType: tc.contentType,
+			})
+
+			if tc.valid {
+				if err != nil {
+					t.Fatalf("expected no error, got %v", err)
+				}
+				if result.ID == 0 {
+					t.Errorf("expected repository-assigned id, got 0")
+				}
+			} else {
+				if err == nil {
+					t.Errorf("expected an unsupported-content-type error, got nil")
+				}
+				if len(repo.images) != 0 {
+					t.Errorf("expected no image stored, got %d", len(repo.images))
+				}
+			}
+		})
+	}
+}
+
+func TestCreateImagePropagatesRepositoryFailure(t *testing.T) {
+	repo := newMockImageRepo()
+	repo.fail.failNext("Create")
+	uc := useCases.NewCreateImageUseCase(repo)
+
+	_, err := uc.CreateImage(imageDomain.ImageInput{
+		Content:     strings.NewReader("data"),
+		Filename:    "test.png",
+		ContentType: "image/png",
+	})
+
+	if !errors.Is(err, errRepositoryFailure) {
+		t.Errorf("expected repository failure, got %v", err)
+	}
+}
+
+func TestDeleteImageRequiresExistence(t *testing.T) {
+	t.Run("id_1", func(t *testing.T) {
+		repo := newMockImageRepo()
+		repo.images[1] = imageDomain.Image{ID: 1}
+		uc := useCases.NewDeleteImageUseCase(repo)
+
+		err := uc.DeleteImage(1)
+		if err != nil {
+			t.Fatalf("expected no error, got %v", err)
+		}
+		if _, exists := repo.images[1]; exists {
+			t.Errorf("expected the image to be removed from the fake")
+		}
+	})
+
+	t.Run("id_9", func(t *testing.T) {
+		repo := newMockImageRepo()
+		repo.images[1] = imageDomain.Image{ID: 1}
+		uc := useCases.NewDeleteImageUseCase(repo)
+
+		err := uc.DeleteImage(9)
+		if !errors.Is(err, gorm.ErrRecordNotFound) {
+			t.Errorf("expected gorm.ErrRecordNotFound, got %v", err)
+		}
+	})
+}
+
+func TestCreateUserAssignsVerificationCode(t *testing.T) {
+	repo := newMockUserRepo()
+	uc := useCases.NewCreateUserUseCase(repo)
+
+	before := time.Now()
+	result, err := uc.CreateUser(useCases.CreateUserCommand{
+		Username: "alice",
+		Password: "hunter2example",
+		Email:    "alice@example.com",
+	})
+	after := time.Now()
+
+	if err != nil {
+		t.Fatalf("expected no error, got %v", err)
+	}
+	if result.ID == 0 {
+		t.Errorf("expected repository-assigned id, got 0")
+	}
+	if result.IsVerified {
+		t.Errorf("expected is_verified false")
+	}
+	if result.VerificationCode == "" {
+		t.Errorf("expected a generated verification code")
+	}
+	if result.PasswordResetCode != "" {
+		t.Errorf("expected empty password_reset_code, got %q", result.PasswordResetCode)
+	}
+	minExpiration := before.Add(2 * time.Hour).Add(-time.Minute)
+	maxExpiration := after.Add(2 * time.Hour).Add(time.Minute)
+	if result.VerificationExpiration.Before(minExpiration) || result.VerificationExpiration.After(maxExpiration) {
+		t.Errorf("expected verification_expiration about 2 hours from now, got %v", result.VerificationExpiration)
+	}
+
+	second, err := uc.CreateUser(useCases.CreateUserCommand{
+		Username: "bob",
+		Password: "hunter2example",
+		Email:    "bob@example.com",
+	})
+	if err != nil {
+		t.Fatalf("expected no error, got %v", err)
+	}
+	if second.VerificationCode == result.VerificationCode {
+		t.Errorf("expected a distinct verification code from the previous call")
+	}
+}
+
+func TestCreateUserPropagatesRepositoryFailure(t *testing.T) {
+	repo := newMockUserRepo()
+	repo.fail.failNext("Create")
+	uc := useCases.NewCreateUserUseCase(repo)
+
+	_, err := uc.CreateUser(useCases.CreateUserCommand{
+		Username: "alice",
+		Password: "hunter2example",
+		Email:    "alice@example.com",
+	})
+
+	if !errors.Is(err, errRepositoryFailure) {
+		t.Errorf("expected repository failure, got %v", err)
+	}
+}
+
+func TestGetUserReadsByIdUsernameOrEmail(t *testing.T) {
+	newRepo := func() *mockUserRepo {
+		repo := newMockUserRepo()
+		repo.users[1] = user.User{ID: 1, Username: "alice", Email: "alice@example.com"}
+		return repo
+	}
+
+	t.Run("GetUser_1", func(t *testing.T) {
+		repo := newRepo()
+		uc := useCases.NewGetUserUseCase(repo)
+		result, err := uc.GetUser(1)
+		if err != nil {
+			t.Fatalf("expected no error, got %v", err)
+		}
+		if result.ID != 1 {
+			t.Errorf("expected user id 1, got %d", result.ID)
+		}
+	})
+
+	t.Run("GetUser_9", func(t *testing.T) {
+		repo := newRepo()
+		uc := useCases.NewGetUserUseCase(repo)
+		_, err := uc.GetUser(9)
+		if !errors.Is(err, gorm.ErrRecordNotFound) {
+			t.Errorf("expected gorm.ErrRecordNotFound, got %v", err)
+		}
+	})
+
+	t.Run("GetUserByUsername_alice", func(t *testing.T) {
+		repo := newRepo()
+		uc := useCases.NewGetUserUseCase(repo)
+		result, err := uc.GetUserByUsername("alice")
+		if err != nil {
+			t.Fatalf("expected no error, got %v", err)
+		}
+		if result.ID != 1 {
+			t.Errorf("expected user id 1, got %d", result.ID)
+		}
+	})
+
+	t.Run("GetUserByUsername_bob", func(t *testing.T) {
+		repo := newRepo()
+		uc := useCases.NewGetUserUseCase(repo)
+		_, err := uc.GetUserByUsername("bob")
+		if !errors.Is(err, gorm.ErrRecordNotFound) {
+			t.Errorf("expected gorm.ErrRecordNotFound, got %v", err)
+		}
+	})
+
+	t.Run("GetUserByEmail_alice", func(t *testing.T) {
+		repo := newRepo()
+		uc := useCases.NewGetUserUseCase(repo)
+		result, err := uc.GetUserByEmail("alice@example.com")
+		if err != nil {
+			t.Fatalf("expected no error, got %v", err)
+		}
+		if result.ID != 1 {
+			t.Errorf("expected user id 1, got %d", result.ID)
+		}
+	})
+
+	t.Run("GetUserByEmail_bob", func(t *testing.T) {
+		repo := newRepo()
+		uc := useCases.NewGetUserUseCase(repo)
+		_, err := uc.GetUserByEmail("bob@example.com")
+		if !errors.Is(err, gorm.ErrRecordNotFound) {
+			t.Errorf("expected gorm.ErrRecordNotFound, got %v", err)
+		}
+	})
+}
+
+func TestListUsersReturnsEveryUser(t *testing.T) {
+	repo := newMockUserRepo()
+	repo.users[1] = user.User{ID: 1}
+	repo.users[2] = user.User{ID: 2}
+	uc := useCases.NewListUsersUseCase(repo)
+
+	result := uc.ListUsers()
+
+	if len(result) != 2 {
+		t.Fatalf("expected 2 users, got %d", len(result))
+	}
+	ids := map[uint32]bool{result[0].ID: true, result[1].ID: true}
+	if !ids[1] || !ids[2] {
+		t.Errorf("expected users with ids 1 and 2, got %+v", result)
+	}
+}
+
+func TestUpdateUserDelegatesEachOperation(t *testing.T) {
+	newRepo := func() *mockUserRepo {
+		repo := newMockUserRepo()
+		repo.users[1] = user.User{ID: 1}
+		return repo
+	}
+
+	t.Run("UpdateVerificationStatus_id1", func(t *testing.T) {
+		repo := newRepo()
+		uc := useCases.NewUpdateUserUseCase(repo)
+		result, err := uc.UpdateVerificationStatus(1, true)
+		if err != nil {
+			t.Fatalf("expected no error, got %v", err)
+		}
+		if result.ID != 1 || !result.IsVerified {
+			t.Errorf("unexpected result: %+v", result)
+		}
+	})
+
+	t.Run("UpdateVerificationStatus_id9", func(t *testing.T) {
+		repo := newRepo()
+		uc := useCases.NewUpdateUserUseCase(repo)
+		_, err := uc.UpdateVerificationStatus(9, true)
+		if !errors.Is(err, gorm.ErrRecordNotFound) {
+			t.Errorf("expected gorm.ErrRecordNotFound, got %v", err)
+		}
+	})
+
+	t.Run("UpdatePassword_id1", func(t *testing.T) {
+		repo := newRepo()
+		uc := useCases.NewUpdateUserUseCase(repo)
+		result, err := uc.UpdatePassword(1, "newpassword123")
+		if err != nil {
+			t.Fatalf("expected no error, got %v", err)
+		}
+		if result.ID != 1 {
+			t.Errorf("expected user id 1, got %d", result.ID)
+		}
+	})
+
+	t.Run("UpdatePassword_id9", func(t *testing.T) {
+		repo := newRepo()
+		uc := useCases.NewUpdateUserUseCase(repo)
+		_, err := uc.UpdatePassword(9, "newpassword123")
+		if !errors.Is(err, gorm.ErrRecordNotFound) {
+			t.Errorf("expected gorm.ErrRecordNotFound, got %v", err)
+		}
+	})
+
+	t.Run("UpdatePasswordResetCode_id1", func(t *testing.T) {
+		repo := newRepo()
+		uc := useCases.NewUpdateUserUseCase(repo)
+		result, err := uc.UpdatePasswordResetCode(1, "reset-code-123")
+		if err != nil {
+			t.Fatalf("expected no error, got %v", err)
+		}
+		if result.ID != 1 {
+			t.Errorf("expected user id 1, got %d", result.ID)
+		}
+	})
+
+	t.Run("UpdatePasswordResetCode_id9", func(t *testing.T) {
+		repo := newRepo()
+		uc := useCases.NewUpdateUserUseCase(repo)
+		_, err := uc.UpdatePasswordResetCode(9, "reset-code-123")
+		if !errors.Is(err, gorm.ErrRecordNotFound) {
+			t.Errorf("expected gorm.ErrRecordNotFound, got %v", err)
+		}
+	})
+}
+
+func TestDeleteUserSucceedsSilently(t *testing.T) {
+	for _, id := range []uint32{1, 9} {
+		t.Run(fmt.Sprintf("id_%d", id), func(t *testing.T) {
+			repo := newMockUserRepo()
+			repo.users[1] = user.User{ID: 1}
+			uc := useCases.NewDeleteUserUseCase(repo)
+
+			err := uc.DeleteUser(id)
+			if err != nil {
+				t.Errorf("expected no error, got %v", err)
+			}
+		})
+	}
+}
+
+func TestSendMailForwardsArgumentsVerbatim(t *testing.T) {
+	cases := []struct {
+		receiver string
+		template string
+	}{
+		{"alice@example.com", "verify-email"},
+		{"bob@example.com", "password-reset"},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.receiver+"_"+tc.template, func(t *testing.T) {
+			repo := newMockMailRepo()
+			uc := useCases.NewSendMailUseCase(repo)
+			data := map[string]string{"key": "value"}
+
+			err := uc.SendMail(tc.receiver, tc.template, data)
+
+			if err != nil {
+				t.Fatalf("expected no error, got %v", err)
+			}
+			if len(repo.SentEmails) != 1 {
+				t.Fatalf("expected exactly one recorded send, got %d", len(repo.SentEmails))
+			}
+			sent := repo.SentEmails[0]
+			if sent.Address != tc.receiver || sent.Template != tc.template {
+				t.Errorf("unexpected recorded send: %+v", sent)
+			}
+			if !reflect.DeepEqual(sent.Data, data) {
+				t.Errorf("expected recorded data %+v, got %+v", data, sent.Data)
+			}
+		})
+	}
+}
+
+func TestSendMailPropagatesRepositoryFailureWithoutRecording(t *testing.T) {
+	repo := newMockMailRepo()
+	repo.fail.failNext("Send")
+	uc := useCases.NewSendMailUseCase(repo)
+
+	err := uc.SendMail("carol@example.com", "welcome", nil)
+
+	if !errors.Is(err, errRepositoryFailure) {
+		t.Errorf("expected repository failure, got %v", err)
+	}
+	if len(repo.SentEmails) != 0 {
+		t.Errorf("expected no send recorded, got %d", len(repo.SentEmails))
+	}
+}
diff --git a/test/user_test.go b/test/user_test.go
index a45eb43..29bf793 100644
--- a/test/user_test.go
+++ b/test/user_test.go
@@ -3,56 +3,137 @@ package test
 import (
 	"RenewCMS/internal/domain/user"
 	"RenewCMS/internal/infrastructure/useCases"
+	"sort"
 	"testing"
+
+	"gorm.io/gorm"
 )
 
 type mockUserRepo struct {
-	users map[uint32]user.User
+	users  map[uint32]user.User
+	nextID uint32
+	fail   failSwitch
+}
+
+func newMockUserRepo() *mockUserRepo {
+	return &mockUserRepo{users: make(map[uint32]user.User)}
+}
+
+func (m *mockUserRepo) sortedIds() []uint32 {
+	ids := make([]uint32, 0, len(m.users))
+	for id := range m.users {
+		ids = append(ids, id)
+	}
+	sort.Slice(ids, func(i, j int) bool { return ids[i] < ids[j] })
+	return ids
+}
+
+func (m *mockUserRepo) Get(id uint32) (user.User, error) {
+	if err := m.fail.trigger("Get"); err != nil {
+		return user.User{}, err
+	}
+	u, ok := m.users[id]
+	if !ok {
+		return user.User{}, gorm.ErrRecordNotFound
+	}
+	return u, nil
+}
+
+func (m *mockUserRepo) GetByUsername(username string) (user.User, error) {
+	if err := m.fail.trigger("GetByUsername"); err != nil {
+		return user.User{}, err
+	}
+	for _, id := range m.sortedIds() {
+		u := m.users[id]
+		if u.Username == username {
+			return u, nil
+		}
+	}
+	return user.User{}, gorm.ErrRecordNotFound
+}
+
+func (m *mockUserRepo) GetByEmail(email string) (user.User, error) {
+	if err := m.fail.trigger("GetByEmail"); err != nil {
+		return user.User{}, err
+	}
+	for _, id := range m.sortedIds() {
+		u := m.users[id]
+		if u.Email == email {
+			return u, nil
+		}
+	}
+	return user.User{}, gorm.ErrRecordNotFound
+}
+
+func (m *mockUserRepo) GetAll() []user.User {
+	result := make([]user.User, 0)
+	for _, id := range m.sortedIds() {
+		result = append(result, m.users[id])
+	}
+	return result
 }
 
 func (m *mockUserRepo) Create(u user.User) (user.User, error) {
-	u.ID = uint32(len(m.users) + 1)
+	if err := m.fail.trigger("Create"); err != nil {
+		return user.User{}, err
+	}
+	m.nextID++
+	u.ID = m.nextID
 	m.users[u.ID] = u
 	return u, nil
 }
 
-func (m *mockUserRepo) Get(id uint32) (user.User, error) {
-	u, ok := m.users[id]
+func (m *mockUserRepo) Delete(id uint32) error {
+	if err := m.fail.trigger("Delete"); err != nil {
+		return err
+	}
+	delete(m.users, id)
+	return nil
+}
+
+func (m *mockUserRepo) UpdateVerificationStatus(userId uint32, isVerified bool) (user.User, error) {
+	if err := m.fail.trigger("UpdateVerificationStatus"); err != nil {
+		return user.User{}, err
+	}
+	u, ok := m.users[userId]
 	if !ok {
-		return user.User{}, nil
+		return user.User{}, gorm.ErrRecordNotFound
 	}
+	u.IsVerified = isVerified
+	m.users[userId] = u
 	return u, nil
 }
 
-func (m *mockUserRepo) GetAll() []user.User {
-	var list []user.User
-	for _, u := range m.users {
-		list = append(list, u)
+func (m *mockUserRepo) UpdatePassword(userId uint32, password string) (user.User, error) {
+	if err := m.fail.trigger("UpdatePassword"); err != nil {
+		return user.User{}, err
 	}
-	return list
-}
-
-func (m *mockUserRepo) UpdateVerificationStatus(id uint32, v bool) (user.User, error) {
-	u := m.users[id]
-	u.IsVerified = v
-	m.users[id] = u
+	u, ok := m.users[userId]
+	if !ok {
+		return user.User{}, gorm.ErrRecordNotFound
+	}
+	u.Password = password
+	m.users[userId] = u
 	return u, nil
 }
 
-func (m *mockUserRepo) GetByUsername(n string) (user.User, error) { return user.User{}, nil }
-func (m *mockUserRepo) GetByEmail(e string) (user.User, error)    { return user.User{}, nil }
-func (m *mockUserRepo) Delete(id uint32) error                    { return nil }
-func (m *mockUserRepo) UpdatePassword(id uint32, p string) (user.User, error) {
-	return user.User{}, nil
-}
-func (m *mockUserRepo) UpdatePasswordResetCode(id uint32, c string) (user.User, error) {
-	return user.User{}, nil
+func (m *mockUserRepo) UpdatePasswordResetCode(userId uint32, code string) (user.User, error) {
+	if err := m.fail.trigger("UpdatePasswordResetCode"); err != nil {
+		return user.User{}, err
+	}
+	u, ok := m.users[userId]
+	if !ok {
+		return user.User{}, gorm.ErrRecordNotFound
+	}
+	u.PasswordResetCode = code
+	m.users[userId] = u
+	return u, nil
 }
 
 var _ user.Repository = &mockUserRepo{}
 
 func TestCreateUser(t *testing.T) {
-	repo := &mockUserRepo{users: make(map[uint32]user.User)}
+	repo := newMockUserRepo()
 	uc := useCases.NewCreateUserUseCase(repo)
 
 	cmd := useCases.CreateUserCommand{
@@ -74,9 +155,8 @@ func TestCreateUser(t *testing.T) {
 }
 
 func TestUpdateUserVerification(t *testing.T) {
-	repo := &mockUserRepo{users: map[uint32]user.User{
-		1: {ID: 1, IsVerified: false},
-	}}
+	repo := newMockUserRepo()
+	repo.users[1] = user.User{ID: 1, IsVerified: false}
 	uc := useCases.NewUpdateUserUseCase(repo)
 
 	res, err := uc.UpdateVerificationStatus(1, true)