refactor: standardize API error handling (#1635)

backend/internal/apperror/error_test.go

@@ -0,0 +1,45 @@
+package apperror
+
+import (
+	"errors"
+	"net/http"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestWrapPreservesCauseWithoutChangingClientMessage(t *testing.T) {
+	cause := errors.New("database connection details")
+	err := Wrap(cause, CodeNotFound, http.StatusNotFound, "User not found")
+
+	require.ErrorIs(t, err, cause)
+	require.Equal(t, "User not found", err.ClientMessage())
+	require.Contains(t, err.Error(), "database connection details")
+}
+
+func TestErrorsMatchByCode(t *testing.T) {
+	err := Wrap(errors.New("database connection details"), CodeAlreadyInUse, http.StatusBadRequest, "email is already in use")
+	wrapped := Wrap(err, CodeInternal, http.StatusInternalServerError, "request failed")
+
+	require.True(t, IsCode(err, CodeAlreadyInUse))
+	require.True(t, IsCode(wrapped, CodeAlreadyInUse))
+	require.ErrorIs(t, err, New(CodeAlreadyInUse, http.StatusBadRequest, "username is already in use"))
+	require.NotErrorIs(t, err, errors.Join(New(CodeAlreadyInUse, http.StatusBadRequest, "username is already in use")))
+	require.False(t, IsCode(wrapped, CodeNotFound))
+}
+
+func TestErrorCopiesFields(t *testing.T) {
+	fields := []FieldError{{Field: "email", Code: "required", Message: "is required"}}
+	err := New(CodeValidationFailed, http.StatusBadRequest, "Request validation failed").WithFields(fields)
+	fields[0].Message = "changed"
+
+	require.Equal(t, "is required", err.Fields()[0].Message)
+}
+
+func TestErrorCopiesDetails(t *testing.T) {
+	err := New(CodeAlreadyInUse, http.StatusBadRequest, "Already in use").WithDetail("property", "email")
+	details := err.Details()
+	details["property"] = "password"
+
+	require.Equal(t, map[string]string{"property": "email"}, err.Details())
+}