diff --git a/backend/shared/domain/errors/errors_test.go b/backend/shared/domain/errors/errors_test.go
index 42d3afd..d2a6d7d 100644
--- a/backend/shared/domain/errors/errors_test.go
+++ b/backend/shared/domain/errors/errors_test.go
@@ -25,12 +25,20 @@ func TestDomainError_Is(t *testing.T) {
 	require.True(t, errors.Is(err, target))
 }
 
+// TestDomainError_Is_DifferentCode ensures errors.Is returns false for different codes.
+func TestDomainError_Is_DifferentCode(t *testing.T) {
+	err := Wrap(CodeForbidden, "nope", nil)
+	target := New(CodeUnauthorized, "other")
+	require.False(t, errors.Is(err, target))
+}
+
 // TestDomainError_NewAndWrapFields verifies fields are set for New and Wrap.
 func TestDomainError_NewAndWrapFields(t *testing.T) {
 	created := New(CodeConflict, "conflict")
 	require.Equal(t, CodeConflict, created.Code)
 	require.Equal(t, "conflict", created.Message)
 	require.Nil(t, created.Err)
+	require.Nil(t, errors.Unwrap(created))
 
 	root := errors.New("root")
 	wrapped := Wrap(CodeInternal, "internal", root)
diff --git a/backend/shared/infra/utils/httputil/errors_test.go b/backend/shared/infra/utils/httputil/errors_test.go
index 90c6d6b..5285ccf 100644
--- a/backend/shared/infra/utils/httputil/errors_test.go
+++ b/backend/shared/infra/utils/httputil/errors_test.go
@@ -46,6 +46,58 @@ func TestMapError(t *testing.T) {
 	}
 }
 
+// TestMapError_AllCodes ensures all known error codes map to expected HTTP status codes.
+func TestMapError_AllCodes(t *testing.T) {
+	cases := []struct {
+		code       errorspkg.ErrorCode
+		statusCode int
+	}{
+		{errorspkg.CodeNotFound, http.StatusNotFound},
+		{errorspkg.CodeQuestionNotFound, http.StatusNotFound},
+		{errorspkg.CodeUserNotFound, http.StatusNotFound},
+
+		{errorspkg.CodeInvalidInput, http.StatusBadRequest},
+		{errorspkg.CodeValidationFailed, http.StatusBadRequest},
+		{errorspkg.CodeInvalidPlayerName, http.StatusBadRequest},
+		{errorspkg.CodeInvalidAnswer, http.StatusBadRequest},
+
+		{errorspkg.CodeUnauthorized, http.StatusUnauthorized},
+		{errorspkg.CodeInvalidToken, http.StatusUnauthorized},
+		{errorspkg.CodeTokenExpired, http.StatusUnauthorized},
+
+		{errorspkg.CodeForbidden, http.StatusForbidden},
+		{errorspkg.CodeMFARequired, http.StatusForbidden},
+		{errorspkg.CodeEmailNotVerified, http.StatusForbidden},
+
+		{errorspkg.CodeConflict, http.StatusConflict},
+		{errorspkg.CodeUserAlreadyExists, http.StatusConflict},
+		{errorspkg.CodeGameInProgress, http.StatusConflict},
+
+		{errorspkg.CodeRateLimitExceeded, http.StatusTooManyRequests},
+
+		{errorspkg.CodeSessionExpired, http.StatusGone},
+		{errorspkg.CodeSessionNotActive, http.StatusGone},
+
+		{errorspkg.CodeMaxAttemptsReached, http.StatusUnprocessableEntity},
+		{errorspkg.CodeNoQuestionsAvailable, http.StatusUnprocessableEntity},
+
+		{errorspkg.CodeInternal, http.StatusInternalServerError},
+	}
+
+	for _, tc := range cases {
+		status, resp := MapError(errorspkg.New(tc.code, "message"))
+		require.Equal(t, tc.statusCode, status)
+		require.Equal(t, tc.code.String(), resp.Code)
+	}
+}
+
+// TestMapError_UnknownCode ensures unknown codes fall back to 500.
+func TestMapError_UnknownCode(t *testing.T) {
+	status, resp := MapError(errorspkg.New(errorspkg.ErrorCode("UNKNOWN"), "oops"))
+	require.Equal(t, http.StatusInternalServerError, status)
+	require.Equal(t, "UNKNOWN", resp.Code)
+}
+
 // TestSendError verifies SendError writes the correct status and payload.
 func TestSendError(t *testing.T) {
 	app := fiber.New()