FlowAssertions (Flow Assertions v0.7.1) View Source

This is a library of assertions for Elixir's ExUnit. It emphasizes two things:

  1. Making tests easier to scan by capturing frequently-used assertions in functions that can be used in a pipeline.

    This library will appeal to people who prefer this:

       VM.ServiceGap.accept_form(params, @institution)
       |> ok_content
       |> assert_valid
       |> assert_changes(id: 1,
                         in_service_datestring: @iso_date_1,
                         out_of_service_datestring: @iso_date_2,
                         reason: "reason")

    ... to this:

       assert {:ok, changeset} = VM.ServiceGap.accept_form(params, @institution)
       assert changeset.valid?
       changes = changeset.changes
       assert changes.id == 1
       assert changes.in_service_datestring == @iso_date_1
       assert changes.out_of_service_datestring == @iso_date_2
       assert changes.reason == "reason"

    The key point here is that all of the assert_* functions in this package return their first argument to be used with later chained functions.

  2. Error messages as helpful as those in the base ExUnit assertions:


Add flow_assertions to your list of dependencies in mix.exs:

def deps do
    {:flow_assertions, "~> 0.6", only: :test},


The easiest way is use FlowAssertions, which imports the most important modules, which are:

(in roughly that order).

If you prefer to alias rather than import, note that all the assertion modules end in A. That way, there's no conflict between the module with map assertions (FlowAssertions.MapA and the Map module itself.

Reading error output

ExUnit has very nice reporting for assertions where a left-hand side is compared to a right-hand side, as in:

assert x == y

The error output shows the values of both x and y, using color-coding to highlight differences.

FlowAssertions uses that mechanism when appropriate. However, it does more complicated comparisons, so the words left and right aren't strictly accurate. So, suppose you're reading errors from code like this:

|> assert_something(expected)
|> assert_something_else(expected)

In the output, left will refer to some value extracted from calculation and right will refer to a value extracted from expected (most likely expected itself).

Defining your own assertions


Change log