beady

A macro for writing tests in a Behaviour Driven (BD) style. Inspired by Catch2.

• Simple (doesn't really do anything except rearrange your tests)
• Provides helpful output for when tests fail
• Works with tokio::test (and other custom test attributes)

Example

use beady::scenario;

#[scenario]
fn pushing_an_element_to_a_vec() {
    #[given(an_empty_vec)] {
        let mut vec = vec![];
        
        #[when(an_element_is_pushed_to_the_vec)] {
            vec.push(7);
            
            #[then(the_vec_should_have_one_element)] {
                assert_eq!(vec.len(), 1);
                
                #[and_then(that_element_should_be_the_pushed_value)]
                assert_eq!(vec[0], 7);
            }
            
            #[and_when(the_vec_is_cleared)] {
                vec.clear();
                
                #[then(the_vec_should_be_empty)]
                assert!(vec.is_empty());
            }
        }
    }
}

Running cargo test we can see that this scenario has generated three tests:

running 3 tests
test pushing_an_element_to_a_vec::given::an_empty_vec::when::an_element_is_pushed_to_the_vec::then::the_vec_should_have_one_element::and::the_element_should_be_the_pushed_value ... ok
test pushing_an_element_to_a_vec::given::an_empty_vec::when::an_element_is_pushed_to_the_vec::and::the_vec_is_cleared::then::the_vec_should_be_empty ... ok
test pushing_an_element_to_a_vec::given::an_empty_vec::when::an_element_is_pushed_to_the_vec::then::the_vec_should_have_one_element ... ok

test result: ok. 3 passed; 0 failed; 0 ignored; 0 measured; 3 filtered out; finished in 0.00s

And if we make one of our asserts intentionally fail then we see a full description of the failing scenario alongside the panic message:

test pushing_an_element_to_a_vec::given::an_empty_vec::when::an_element_is_pushed_to_the_vec::then::the_vec_should_have_one_element::and::the_element_should_be_the_pushed_value ... FAILED

failures:

---- pushing_an_element_to_a_vec::given::an_empty_vec::when::an_element_is_pushed_to_the_vec::then::the_vec_should_have_one_element::and::the_element_should_be_the_pushed_value stdout ----

Scenario: pushing an element to a vec
   Given: an empty vec
    When: an element is pushed to the vec
    Then: the vec should have one element
     and: the element should be the pushed value

thread 'pushing_an_element_to_a_vec::given::an_empty_vec::when::an_element_is_pushed_to_the_vec::then::the_vec_should_have_one_element::and::the_element_should_be_the_pushed_value' panicked at 'assertion failed: `(left == right)`
  left: `7`,
 right: `8`'

Usage

Inspired by the BDD-style test cases from Catch2, you can annotate a function with #[scenario] to make it a test, and then use the #[given], #[when], and #[then] attributes to describe the test. Dependent clauses can be specified with the #[and_given], #[and_when], and #[and_then] attributes.

#[scenario]

By default the #[scenario] attribute will generate tests like:

#[test]
fn foo() { ... }

If you want to use another test attribute you can specify it after the #[scenario] attribute like so:

#[scenario]
#[tokio::test]
async fn my_scenario() { ... }

Which will generate tests like:

#[tokio::test]
async fn foo() { ... }