feat: characterized the existing use cases as a baseline; every repo fake behaves like the real ones and can be told to fail, every use case is covered; gremlins runs clean on useCases

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)
 		}
 	})
 }