How to Test OpenUI5 Controls with QUnit
Comprehensive overview of QUnit testing for controls.
Dos and Don’ts
- When writing QUnits, always keep your tests atomic.
- Don’t rely on the execution of previous tests.
- Don’t introduce globals, destroy controls after creating them.
- Only test one single thing.
- When writing a test, always make sure you break it first: don’t rely on tests that have never failed!
- Write human readable tests - use descriptive names for variables. Readability is more important than performance. You don’t have to write a reuse for everything. It’s ok to repeat yourself in unit tests if it helps readability.
- Don’t test too many internal aspects: try to test the control like an application or user will use it.
- You have to find a balance between not stubbing / expecting too much of the internal aspects and not doing it at all. If you tightly couple your test to the implementation, maintenance will be a pain.
- If your test is too long, you’re squeezing too much stuff into one of your control’s functions. Divide the complexity, then your test will be simpler and your productive code will be better.
- Don’t test general OpenUI5 functionality. Only test things actually done by your control (see “What Should You Test?” below).
- Never write an
if in a test. It is a sign that you’re either not stubbing correctly or you’re testing multiple things in one test.
- Use the
expect QUnit statement to specify how many assertions are expected. You should always write your test in a way that every assertion will be executed. This is especially important if you want to test asynchronous behavior. Using expect helps you find out if all asynchronous operations have been resolved and all expected code paths have been passed.
- Whenever you encounter a Bug/Ticket, start by writing a QUnit that fails first, and then fix the code.
- Write your tests as small as possible: don’t add a statement that is not needed for the test, such as an ID in the control’s constructor properties.
- Use fake timers to avoid as many async tests as possible.
- Don’t test the exact same thing multiple times.
- Use modules for grouping your tests: this will give you a better organizational test setup.
- You may use modules for
beforeEach/afterEach, but don’t overuse this feature. If you have a longer module, you might not see what the test does because you don’t know its setup.
- It’s sometimes better to write code multiple times.
- Don’t set up your system being tested in the
beforeEach/afterEach. It is very rare that all tests in a module have the same constructor. Furthermore, using a global constructor object is dangerous.
If you stick to these rules, you will find it much easier to refactor/maintain your tests. Keeping the tests atomic will make debugging much easier, because you will hit your breakpoints for the code being tested only. If you write QUnits without keeping to these rules, you may well not notice anything bad to begin with, but you will eventually end up in the middle of a maintenance nightmare!
Arrange Act Assert Pattern
Internally, we use three templates for testing. The one shown below is the general control template.
Use the following pattern to structure your tests. If everyone sticks to this same pattern, you will be able to read your colleagues’ tests very quickly:
QUnit.test("Should do Something", function (assert) {
// Arrange
// System under Test
var oMyControl = new nameSpace.myControl({
});
// Act
// Assert
// Cleanup
oMyControl.destroy();
});
Arrange
In Arrange, you should set up the dependencies and options you need for your System under Test.
Examples:
- The constructor object of your control
- Sinon spies/stubs and mocks (dependencies of your System under Test)
- Model
System under test
In System under Test, you should create your control and you should also render it if you want to test the rendering.
Act
Ideally, this part is only one single line of code executing the function you want to test.
Assert
This part may contain multiple statements of QUnit assertions, but ideally not too many in total.
Make sure that you also test negative paths, not only the expected ones.
Optional: Cleanup
Here you should destroy all the controls/models you created.
If you don’t use Sinon sandboxes, revert all the spies/stubs/mocks.
What Should You Test?
- Test all the public functions you introduced.
- Test all the overwritten getters and setters.
- Test your control’s events and how often they are called.
- Test all possible user interactions (tap, keyboard, focus).
- You could test how often your control gets rerendered when interacting with it, but only if you are worried that it might be rerenderd too often or not at all.
- Test RTL if you have special things done in javascript.
- Write some integration tests if you have a composite control (don’t cover 100% of your child controls - that’s overkill and child controls will be hard to maintain).
- You may test default values of properties, since we cannot change them backwards afterwards and a test will recognize this.
- Test how your control interacts with models (OData + Json).
- Test the destruction of your control when working with composites, test if all dependencies/events are unbound on destruction.
What Should You NOT Test?
- Never test non-overwritten getters and setters (these are tested in the core of the framework).
- Never test your complete CSS with computed styles: just check if the classes are set correctly. Focus on testing JavaScript.
- Never test other generic framework functionality. Focus on your control.
Pitfalls
Sinon fake timers
Using fake timers can be error-prone. Fake timers should only be used with care in specific scenarios. In order to avoid pitfalls using fake timers, see the following documentation:
I’ve set a property on my control: Why aren’t the changes in the DOM?
The most likely reason for this is that it didn’t wait for the sap/ui/test/utils/nextUIUpdate Promise. OpenUI5 does not render synchronously, but waiting for the Promise will proceed the test after the rendering is done.
For more information, see Rendering and Re-rendering Controls Within Tests
- [Cookbook for Testing Controls with QUnit](cookbook-for-testing-controls-with-qunit-0ddcc60.md “”)