Add edge case unit tests for OAuth2TokenManager

- Introduced new test cases in `OAuth2TokenManager` to handle edge cases for negative, zero, and very small expiry dates, ensuring the `isTokenValid` method correctly identifies invalid token data.
- These tests enhance the robustness of the token validation logic by covering additional scenarios that could lead to incorrect token handling.

This update improves the overall reliability of the OAuth2 token management implementation by validating critical edge cases in token expiry handling.

Author: anatolyshipitz

workers/main/src/services/OAuth2/OAuth2TokenManager.errors.test.ts

@@ -36,7 +36,6 @@ describe('OAuth2TokenManager - Error Handling', () => {
 
   beforeEach(async () => {
     tokenManager = new OAuth2TokenManager('qbo', 'test-refresh-token');
-    // Wait for async initialization to complete
     await new Promise((resolve) => setTimeout(resolve, 0));
   });
 
@@ -113,4 +112,42 @@ describe('OAuth2TokenManager - Error Handling', () => {
       );
     });
   });
+
+  describe('edge cases', () => {
+    it('should handle negative expiry date', () => {
+      const tokenData: TokenData = {
+        access_token: 'valid-token',
+        refresh_token: 'refresh-token',
+        expires_at: -1000,
+        token_type: 'Bearer',
+      };
+
+      tokenManager.setTokenDataForTesting(tokenData);
+      expect(tokenManager.isTokenValid()).toBe(false);
+    });
+
+    it('should handle zero expiry date', () => {
+      const tokenData: TokenData = {
+        access_token: 'valid-token',
+        refresh_token: 'refresh-token',
+        expires_at: 0,
+        token_type: 'Bearer',
+      };
+
+      tokenManager.setTokenDataForTesting(tokenData);
+      expect(tokenManager.isTokenValid()).toBe(false);
+    });
+
+    it('should handle very small expiry date', () => {
+      const tokenData: TokenData = {
+        access_token: 'valid-token',
+        refresh_token: 'refresh-token',
+        expires_at: Number.MIN_SAFE_INTEGER,
+        token_type: 'Bearer',
+      };
+
+      tokenManager.setTokenDataForTesting(tokenData);
+      expect(tokenManager.isTokenValid()).toBe(false);
+    });
+  });
 });