Collections

September 30, 2023 ยท View on GitHub

While you can use Clojure's standard functions to manipulate collections of data to build up your tests, Expectations provides some conveniences to make life a bit easier: in and from-each.

expect in

If you have a function that returns a hash map but you only care about testing certain parts of it, you can write an expectation like this:

  (expect {:membership/status "active" :membership/type "platinum"}
          (in (lookup-membership db-spec test-user)))

This says "we expect the following key/value pairs to be in the result".

You can also use in with sets, lists, and vectors:

  (expect "platinum" (in (membership-types db-spec)))

It's worth noting that the default output from in can be somewhat confusing and this is definitely a case where Humane Test Output helps:

  (expect {:foo 1} (in {:bar 2}))

;; default output
FAIL in () (...:...)
(in {:bar 2})

expected: (expect {:foo 1} (in {:bar 2}))
  actual: (not= {:foo 1} {})

;; with Humane Test Output:
FAIL in () (...:...)
(in {:bar 2})

expected: {:foo 1}
  actual: {}
    diff: - {:foo 1}

This is an area that will be improved in the future.

expect from-each

If you have an expectation that should apply to every element of a collection, such as expecting all active-users to have memberships that have an "active" status, we can write this:

  (expect {:membership/status "active"}
          (from-each [user (find-active-users db-spec)]
            (in (lookup-membership db-spec user))))

from-each is effectively a shorthand for a test that would otherwise look like this:

  (doseq [user (find-active-users db-spec)]
    (expect {:membership/status "active"}
            (in (lookup-membership db-spec user))))

A simpler from-each example:

  (expect even? (from-each [n (range 10)] (* 2 n)))

from-each also supports :let and :when syntax just like for and doseq.

See also Expecting More for examples of combining from-each with other Expectations for powerful multi-valued tests.

Further Reading