In order to fix a bug in an application, I modified a method named `postLogin` by adding a call to an existing method named `getShoppingCart`. 

**Code**

```
protected void postLogin() {
  getShoppingCart();
}

```

However, I'm not sure what the best way to write a unit test for `postLogin` is. 

**Approach 1**

Use verify from Mockito to simply verify that the method was called.

```
verify(mock).getShoppingCart();

```

**Approach 2**

Test the side effect of the method call by fetching the value of the user's shopping cart.

```
AssertNotNull(user.getShoppingCart());

```

Is one approach better than the other?