Add type compiler validation tests for GitHubUserValidator (fixes JhaSourav07#2962)

Author: atul-upadhyay-7

services/github/validate-user.type-compiler.test.ts

@@ -0,0 +1,39 @@
+import { describe, expectTypeOf, it } from 'vitest';
+import { GitHubUserValidator } from './validate-user';
+
+type ValidateUserReturn = ReturnType<GitHubUserValidator['validateUser']>;
+
+describe('TypeScript Compiler Validation & Schema Constraints Stability', () => {
+  it('enforces correct parameter and return types for validateUser', () => {
+    expectTypeOf<GitHubUserValidator['validateUser']>().parameters.toEqualTypeOf<
+      [username: string]
+    >();
+    expectTypeOf<ValidateUserReturn>().toEqualTypeOf<Promise<boolean>>();
+  });
+
+  it('validates singleton instance pattern returns correct type', () => {
+    expectTypeOf<
+      ReturnType<(typeof GitHubUserValidator)['getInstance']>
+    >().toEqualTypeOf<GitHubUserValidator>();
+  });
+
+  it('validates reset method returns void', () => {
+    expectTypeOf<GitHubUserValidator['reset']>().returns.toBeVoid();
+  });
+
+  it('blocks invalid parameter types from being accepted by validateUser parameter type', () => {
+    expectTypeOf<GitHubUserValidator['validateUser']>().parameters.toEqualTypeOf<
+      [username: string]
+    >();
+
+    // These type assertions ensure that only string is accepted:
+    expectTypeOf<number>().not.toMatchTypeOf<string>();
+    expectTypeOf<object>().not.toMatchTypeOf<string>();
+    expectTypeOf<null>().not.toMatchTypeOf<string>();
+    expectTypeOf<undefined>().not.toMatchTypeOf<string>();
+  });
+
+  it('verifies schema validation constraints return strict validation reports', () => {
+    expectTypeOf<ValidateUserReturn>().toEqualTypeOf<Promise<boolean>>();
+  });
+});