Testing
Testing is a crucial part of developing software. It can help prevent regressions and ensure stability. Remember, good tests should grow with your project. If you’re constantly having to change or fiddle with your tests, this is a sign that you may be testing the wrong things.
Gleam’s test runner, gleeunit, binds to Erlang’s EUnit framework and provides a simple interface to it. If gleeunit isn’t already configured (new Gleam projects have it by default), follow the set up instructions in the documentation.
How and What to Test
For some reason, software testing is a very personal, dogmatic issue. Some people swear by 100% code coverage, others don’t test at all; most people are probably somewhere between the two extremes. The usefulness of testing depends on what you’re building. Something error-prone like a parser should have tons of tests to prevent regressions. A web app may need significantly less.
Be pragmatic here — don’t box yourself into a corner with code coverage goals or brittle tests. Or ignore my advice, either way.
There’s many kinds of testing, but the general categories are:
- Unit testing
- Integration testing
- End-to-end testing
As of writing, Gleam doesn’t really have tooling for integration and E2E testing. So for now, we’ll focus on unit testing.
Unit Testing
Unit testing is about testing small components of your software. Each test should have a relatively small surface area. This way, you can understand the potential issue when a test breaks.
A gleeunit test is a function with a name ending in _test. The test passes by returning an arbitrary value (ignored by the test runner), or fails by crashing or panicking. Since panics and assertions will cause a test to fail, we can use idiomatic Gleam in our tests:
pub fn results_test() {
let assert Ok(_) = function_that_might_fail()
}However, gleeunit provides utilities for these common cases. The utilities provide better error messages and a readable, standardized interface. gleeunit.should provides common testing helpers for checking equality, booleans, Results, and Options.