fix(#411): added redirect to login/page.tsx to redirect users (#437)

- Added `useRouter` to the login page so users get redirected to
`/league/all` if they are already signed in and navigate to `/login`.
- Added unit test for the `route.push` function as well.

app/(main)/login/page.test.tsx

@@ -78,4 +78,12 @@ describe('Login', () => {
 
     mockUseAuthContext.isSignedIn = false;
   });
-});
+
+  test('redirects to /league/all when user navigates to /login', async () => {
+    mockUseAuthContext.isSignedIn = true;
+
+    render(<Login />);
+
+    expect(mockPush).toHaveBeenCalledWith('/league/all');
+  });
+});

app/(main)/login/page.tsx

@@ -55,6 +55,7 @@ const Login = (): React.JSX.Element => {
   useEffect(() => {
     if (isSignedIn) {
       getUser();
+      router.push('/league/all');
     }
   }, [isSignedIn, getUser]);