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Test if a function throws? #92

lazarljubenovic opened this issue Mar 11, 2017 · 2 comments


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commented Mar 11, 2017

It would be really nice to add ability to test if a function throws (like expect(...).toThrow('error message').


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commented Mar 11, 2017

I agree. Here's how we did it in Susy. I don't feel like I can ship that as part of True, because it adds a function to your production code. I don't want True to be a production dependency, so it's better if that function lives outside True.

Add a variable and function like these to your project:

$_test-environment: false;

@function _error(
  $capture: $_test-environment
) {
  @if $capture {
    @return 'ERROR: #{$message}';

  @error '#{$message}';

Return that function wherever you would normally @error:

// what you had before...
@error "that won't work at all, please try again";

// what you use now...
@return _error("that won't work at all, please try again");

In your production code, set $_test-environment: false; and then change it to true in your testing environment. Suddenly failing functions will return error messages you can test for:

  @include test('Error on invalid thing') {
    @include assert-equal(
      "ERROR: that won't work at all, please try again"

Does that make sense? If you have ideas for a better way to do that without adding production requirements, I'm all ears!


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commented Mar 11, 2017

Aaah, this is one of those tricks that are so obvious once someone tells you about them. Yeah, it makes perfect sense. Thanks for sharing the idea!

It's indeed tricky to do anything similar without adding a production dep 😐 If I experience some kind of sudden enlightenment, I'll make sure to drop by with an idea or two 😄

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