test: cover json tag display and whitespace required case

internal/validation/validation.go

@@ -175,6 +175,33 @@ type FieldValidationError struct {
 	Message string
 }
 
+func getFieldDisplayName(field reflect.StructField) string {
+	jsonTag := field.Tag.Get("json")
+	if jsonTag != "" && jsonTag != "-" {
+		if idx := strings.Index(jsonTag, ","); idx != -1 {
+			jsonTag = jsonTag[:idx]
+		}
+		if jsonTag != "" {
+			return jsonTag
+		}
+	}
+	return camelCaseToWords(field.Name)
+}
+
+func camelCaseToWords(s string) string {
+	if s == "" {
+		return s
+	}
+	var result strings.Builder
+	for i, r := range s {
+		if i > 0 && unicode.IsUpper(r) {
+			result.WriteRune(' ')
+		}
+		result.WriteRune(unicode.ToLower(r))
+	}
+	return result.String()
+}
+
 func ValidateStruct(s interface{}) error {
 	if s == nil {
 		return nil
@@ -232,9 +259,10 @@ func ValidateStruct(s interface{}) error {
 				tagName = tag
 			}
 
-			if err := validateField(field.Name, fieldVal, tagName, param, omitempty); err != nil {
+			displayName := getFieldDisplayName(field)
+			if err := validateField(displayName, fieldVal, tagName, param, omitempty); err != nil {
 				errors = append(errors, FieldValidationError{
-					Field:   field.Name,
+					Field:   displayName,
 					Tag:     tagName,
 					Param:   param,
 					Message: err.Message,
@@ -293,7 +321,7 @@ func validateField(fieldName string, fieldVal reflect.Value, tagName, param stri
 func isEmptyValue(v reflect.Value) bool {
 	switch v.Kind() {
 	case reflect.String:
-		return v.String() == ""
+		return strings.TrimSpace(v.String()) == ""
 	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
 		return v.Int() == 0
 	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
@@ -301,7 +329,7 @@ func isEmptyValue(v reflect.Value) bool {
 	case reflect.Float32, reflect.Float64:
 		return v.Float() == 0
 	case reflect.Bool:
-		return !v.Bool()
+		return false
 	case reflect.Pointer, reflect.Interface, reflect.Slice, reflect.Map:
 		return v.IsNil()
 	default:
@@ -317,7 +345,8 @@ func validateMin(fieldName string, v reflect.Value, param string) *ValidationErr
 
 	switch v.Kind() {
 	case reflect.String:
-		if len(v.String()) < min {
+		s := strings.TrimSpace(v.String())
+		if len([]rune(s)) < min {
 			return &ValidationError{Field: fieldName, Message: fmt.Sprintf("%s must be at least %d characters", fieldName, min)}
 		}
 	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
@@ -344,7 +373,7 @@ func validateMax(fieldName string, v reflect.Value, param string) *ValidationErr
 
 	switch v.Kind() {
 	case reflect.String:
-		if len(v.String()) > max {
+		if len([]rune(v.String())) > max {
 			return &ValidationError{Field: fieldName, Message: fmt.Sprintf("%s must be at most %d characters", fieldName, max)}
 		}
 	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:

internal/validation/validation_test.go

@@ -250,12 +250,12 @@ func TestSanitizeString(t *testing.T) {
 
 func TestValidateStruct(t *testing.T) {
 	type TestStruct struct {
-		Username string `validate:"required,min=3,max=20"`
-		Email    string `validate:"required,email"`
-		Age      int    `validate:"min=18,max=120"`
-		URL      string `validate:"url"`
-		Status   string `validate:"oneof=active inactive pending"`
-		Optional string `validate:"omitempty,min=1"`
+		Username string `json:"username" validate:"required,min=3,max=20"`
+		Email    string `json:"email" validate:"required,email"`
+		Age      int    `json:"age" validate:"min=18,max=120"`
+		URL      string `json:"url" validate:"url"`
+		Status   string `json:"status" validate:"oneof=active inactive pending"`
+		Optional string `json:"optional" validate:"omitempty,min=1"`
 	}
 
 	t.Run("valid struct", func(t *testing.T) {
@@ -287,6 +287,9 @@ func TestValidateStruct(t *testing.T) {
 			if len(structErr.Errors) == 0 {
 				t.Error("Expected validation errors, got none")
 			}
+			if structErr.Errors[0].Message != "username is required" {
+				t.Errorf("Expected JSON tag name in error, got %q", structErr.Errors[0].Message)
+			}
 		}
 	})
 
@@ -318,6 +321,20 @@ func TestValidateStruct(t *testing.T) {
 		}
 	})
 
+	t.Run("whitespace required field", func(t *testing.T) {
+		s := TestStruct{
+			Username: "   ",
+			Email:    "test@example.com",
+			Age:      25,
+			URL:      "https://example.com",
+			Status:   "active",
+		}
+		err := ValidateStruct(s)
+		if err == nil {
+			t.Error("ValidateStruct() expected error, got nil")
+		}
+	})
+
 	t.Run("invalid max", func(t *testing.T) {
 		s := TestStruct{
 			Username: strings.Repeat("a", 21),