[FSSDK-11238] string value validator test addition

Author: junaed-optimizely

lib/utils/string_value_validator/index.spec.ts

@@ -0,0 +1,32 @@
+/**
+ * Copyright 2025, Optimizely
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+import { describe, it, expect } from 'vitest';
+import { validate } from './';
+
+describe('validate', () => {
+  it('should validate the given value is valid string', () => {
+		expect(validate('validStringValue')).toBe(true);
+  });
+
+  it('should return false if given value is invalid string', () => {
+		expect(validate(null)).toBe(false);
+		expect(validate(undefined)).toBe(false);
+		expect(validate('')).toBe(false);
+		expect(validate(5)).toBe(false);
+		expect(validate(true)).toBe(false);
+		expect(validate([])).toBe(false);
+  });
+});