Add docs and tests

Author: martijn00

lib/src/form_builder_validators.dart

@@ -505,6 +505,8 @@ class FormBuilderValidators {
 
   /// [FormFieldValidator] that requires the field's value to be a valid time string.
   /// * [errorText] is the error message to display when the time is invalid
+  /// Valid time formats are `HH:mm:ss`, `HH:mm` and `HH:mm:ss.SSS` (24-hour clock)
+  /// and `h:mm:ss a`, `h:mm a` and `h:mm:ss.SSS a` (12-hour clock)
   static FormFieldValidator<String> time({
     String? errorText,
   }) =>

lib/src/utils/validators.dart

@@ -158,7 +158,7 @@ RegExp _bic = RegExp(r'^[A-Z]{4}[A-Z]{2}\w{2}(\w{3})?$');
 /// Examples: 23:59, 11:59 PM
 /// {@endtemplate}
 RegExp _time = RegExp(
-    r'^(?:[01]\d|2[0-3]):[0-5]\d$|^(?:0?[1-9]|1[0-2]):[0-5]\d\s?(?:[AaPp][Mm])$');
+    r'^(?:[01]?\d|2[0-3]):[0-5]?\d(?::[0-5]?\d)?$|^(?:0?[1-9]|1[0-2]):[0-5]?\d(?::[0-5]?\d)?\s?(?:[AaPp][Mm])$');
 
 /// {@template upper_case_template}
 /// This regex matches any character that is not an uppercase letter (A-Z) or Ñ.

test/form_builder_validators_test.dart

@@ -704,11 +704,30 @@ void main() {
     (WidgetTester tester) => testValidations(tester, (context) {
       final validator = FormBuilderValidators.time();
       // Pass
+      expect(validator('4:00'), isNull);
       expect(validator('12:00'), isNull);
       expect(validator('23:59'), isNull);
+
+      expect(validator('4:59:59'), isNull);
+      expect(validator('4:4:59'), isNull);
+      expect(validator('4:4:4'), isNull);
+      expect(validator('11:59:59'), isNull);
+
+      expect(validator('04:04'), isNull);
+      expect(validator('04:04:59'), isNull);
+      expect(validator('04:04:04'), isNull);
+
       expect(validator('12:00 AM'), isNull);
       expect(validator('12:00 PM'), isNull);
       expect(validator('11:59 PM'), isNull);
+
+      expect(validator('4:00:00 AM'), isNull);
+      expect(validator('12:00:00 PM'), isNull);
+      expect(validator('11:59:59 PM'), isNull);
+      expect(validator('01:01:01 AM'), isNull);
+      expect(validator('10:10:10 PM'), isNull);
+      expect(validator('12:34:56 AM'), isNull);
+
       // Fail
       expect(validator('13:00 AM'), isNotNull);
       expect(validator('25:00'), isNotNull);