Posted by Pete McBreen 04 Jun 2022 at 23:06
Rails and Phoenix introduced the idea of testing to web development, see Rails Guide and Hexdocs Testing Guide their main focus is on Unit Testing, Testing Views and Testing Controllers, while not saying much about System testing. They both make a nod towards Integration testing, but the focus is more on what developers should know about testing rather than a full system test.
With Unit Tests, the test case setup and teardown is relatively minimal, so often a unit test will have a single assertion – basically a unit test is testing just a single thing. This is appropriate for a Unit Test, since the execution time for the test suite is relatively insensitive to the the number of tests when the testing framework can execute a suite of 1,000 unit tests in a few seconds.
For Controller and View tests, both Rails and Phoenix have a nice way of mocking out the webserver interaction so that the behavior of the Controller that responds to the GET/POST/PUT/DELETE requests from the browser can be tested without needing the full stack. Both include the idea of a Test Database for use by the test suite that gets populated by fixtures that work in conjunction with the test cases to provide appropriate data for the tests. Typically the data is set up before each test case and then cleaned up after each test case so that the failure of one test case does not impact the other test cases. Typically these tests run slower than Unit tests, but a reasonable suite of several hundred tests can run in less than 10 seconds.
Both Unit and the Controller/View tests tend to be relatively simple with few assertions. System Testing is different. For a start the setup and teardown time for these tests can be significant, especially if you have a microservice architecture and the test case covers the interactions between multiple services. So system tests have to pay back the larger setup and teardown time by doing more work inside each system test case which means
- the scenario for a system test case has to be more of a Soap Opera
- there should be many more assertions about the steps along the scenario so that if there is an error, the source of the error can be found quickly
- the scenarios should follow multiple alternate paths through the system