test: restore coverage lost to strict-null-check test removals

Several not-found/no-op branches (getTransactionForCreator, SignersService.getSignatureById, UserKeysService.removeKey) lost their tests when strict null checks made the old null-argument mocks stop compiling; re-added equivalent tests using valid inputs (empty result, falsy id, null resolve) instead of the now-illegal null args.

Signed-off-by: John Bair <john.bair@swirldslabs.com>

Author: jbair06

back-end/apps/api/src/transactions/signers/signers.service.spec.ts

@@ -138,6 +138,12 @@ describe('SignersService', () => {
         withDeleted: true,
       });
     });
+
+    it('should return null if id not provided', async () => {
+      const result = await service.getSignatureById(0);
+
+      expect(result).toBeNull();
+    });
   });
 
   describe('getSignaturesByUser', () => {

back-end/apps/api/src/transactions/transactions.service.spec.ts

@@ -3181,6 +3181,14 @@ describe('TransactionsService', () => {
       jest.resetAllMocks();
     });
 
+    it('should throw TNF if no transaction is found', async () => {
+      transactionsRepo.find.mockResolvedValueOnce([]);
+
+      await expect(service.getTransactionForCreator(1, user as User)).rejects.toThrow(
+        ErrorCodes.TNF,
+      );
+    });
+
     it('should throw if user is not the creator', async () => {
       const transaction = { creatorKey: { userId: 231232 } };
 

back-end/apps/api/src/user-keys/user-keys.service.spec.ts

@@ -255,6 +255,12 @@ describe('UserKeysService', () => {
   });
 
   describe('removeKey', () => {
+    it('should throw BadRequestException if the key does not exist', async () => {
+      repo.findOne.mockResolvedValue(null);
+
+      await expect(service.removeKey(1)).rejects.toThrow(ErrorCodes.KNF);
+    });
+
     it('should soft remove the user key if it exists', async () => {
       const userKey = { id: 1, publicKey: 'test-public-key' } as UserKey;
       repo.findOne.mockResolvedValue(userKey);