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/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
+}