Only having one assertion statement in a functional test?

Question

This question is similar to this one but regarding functional tests rather than unit tests.

I'm currently testing a UI using Selenium and I was wondering if only one assertion statement is needed, or if it depends on the test.

For example if I wanna test a basic Facebook login, would it suffice just use an assertion statement for the end case (ex: finding an element that only exists when logged in) or should the test be more detailed and include more than one assertion statement (check if you're on the correct site, check inputs, check for an element that only exists when logged in, etc).

Answer 1

Let me try to answer your Questions one by one:

1. if only one assertion statement is needed, or if it depends on the test - Let us speak of a manual Testcase. A Testcase consists of several steps but at the end we do cross check the Actual Result against the Expected Result. The same ideology is implemented in Automation through assertions. So ideally as per best practices, an assertion statement is a must but it's not mandatory.

2. should the test be more detailed and include more than one assertion statement - You can always have multiple assertions in a Testcase. No issues in that. But you must remember, if one Assertions fails the rest of the assertions won't be executed. Which gives you a single result either Pass or Fail. Now if you want to keep multiple validation points then you have to take help of if/else block so all your validations gets executed irrespective of each of them Pass/Fail.

Let me know if this Answers your query.

Answer 2

The one assertion per testcase rule is bit over the top for functional tests. For functional end-to-end tests I think as a general guide it should be test only ONE behavior. Use as many asserts you need to verify this ONE behavior.

If a test is failing you want to understand what is not working without reading the actual test-code. Having multiple assertions in a single test could lead to testing multiple behaviors and multiple reasons to fail. This is sub-optimal.

Do be practical as functional end-to-end tend to be slow. Multiplying the same steps to test a slightly different assert seems a waste of run time. Your test-suites should also be fast if you want to run them on each check-in. Therefor don't write too many tests on this level. Keep a good balance as the test-pyramid suggests.

For your example I think one assert would be enough. The behavior is to check if the user is now logged in, not if all the elements are on the page. Also keep in mind if the implementation of the site changes you need to update all your tests. The less you assert to more maintainable your tests will be.