test(luthor): Add tests for map validator

packages/luthor/test/validations/map_validation_test.dart

@@ -0,0 +1,48 @@
+import 'package:luthor/luthor.dart';
+import 'package:test/test.dart';
+
+void main() {
+  test('should return true when value is a map', () {
+    final result = l.map().validateValue({});
+
+    switch (result) {
+      case SingleValidationSuccess(data: _):
+        expect(result.data, {});
+      case SingleValidationError(data: _, errors: _):
+        fail('should not have errors');
+    }
+  });
+
+  test('should return false when value is not a map', () {
+    final result = l.map().validateValue('a');
+
+    switch (result) {
+      case SingleValidationSuccess(data: _):
+        fail('should not be a success');
+      case SingleValidationError(data: _, errors: final errors):
+        expect(errors, ['value must be a Map']);
+    }
+  });
+
+  test('should return true when value is null', () {
+    final result = l.map().validateValue(null);
+
+    switch (result) {
+      case SingleValidationSuccess(data: _):
+        expect(result.data, isNull);
+      case SingleValidationError(data: _, errors: _):
+        fail('should not have errors');
+    }
+  });
+
+  test('should return false if the value is null with required()', () {
+    final result = l.required().map().validateValue(null);
+
+    switch (result) {
+      case SingleValidationSuccess(data: _):
+        fail('should not be a success');
+      case SingleValidationError(data: _, errors: final errors):
+        expect(errors, ['value is required']);
+    }
+  });
+}