Smarter Testing with Macros
Learn to create a mini testing framework in Elixir using macros.
If you’re familiar with writing tests in most mainstream languages, you know it can take a while to learn the different assertion functions of testing frameworks.
For example, let’s see how a few basic assertions for popular test frameworks in Ruby and JavaScript compare to Elixir. We don’t need to be familiar with these languages; just be mindful of the different assertion APIs.
Notice how such simple assertions took on arbitrary method and function names in Ruby and JavaScript? They might read nicely, but they subtly mask the expression we are testing. They also require a new mental model for each test framework on how assertions should be made for the given expression.
#Javascriptexpect(value).toBe(true);expect(value).toEqual(12);expect(value).toBeGreaterThan(100);#Rubyassert valueassert_equal value, 12assert_operator value, :<=, 100#Elixirassert valueassert value == 12assert value <= 100
The reason these languages require methods and functions like this is to ensure relevant failure messages. If an assertion like assert value <= 100 failed in Ruby, we would only receive a less than helpful “expected true, got false” test output. Ruby can generate correct failure messages by providing unique functions per the assertion, but it comes at the cost of a larger testing API. We also take on the mental overhead of which function is required each time to write an assertion. There’s a better way.
Macros power Elixir’s ExUnit test framework. As we’ve seen, they give us access to the internal representation of any Elixir ...