Elixir testing libraries with nested contexts, superior readability, and ease of use
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README.md

ShouldI

ExUnit is fine for small, simple applications, but when you want to do more complex test cases, it has limitations. ShouldI provides nested contexts to eliminate duplication in tests, and has better support for naming tests based on behavior. This API is based on the shoulda framework for Ruby on Rails.

Quick start

Just add the hex dependency to your mix file:

defp deps do
  [{:shouldi, only: :test}]
end

and add

...
use ShouldI
...

to your test script in place of

...
use ExUnit.Case
...

Name tests with should

When you're testing behavior, you can get better names with a more descriptive macro. The test code...

test "should return ok on parse" do
  assert :ok == Parser.parse
end

...can become more descriptive and shorter with...

should "return :ok on parse" do
   assert :ok == Parser.parse
end

Nest your context using having

Say you have a test case that needs some setup. ExUnit has support for a context that can be set once, and passed to all clients. You can use the setup method to pass a map to each of your test cases, like this:

defmodule MyFlatTest do
  setup context do
    {:ok, Dict.put context, :necessary_key, :necessary_value}
  end

  test( "this test needs :necessary_key", context ) do
    assert context.necessary_key == :necessary_value
  end
end

This approach breaks down when several, but not all, tests need the same set of values. ShouldI solves this problem with nested contexts, which you can provide with the having keyword, like this:

defmodule MyFatTest do

  having "necessary_key" do
    setup context do
      Dict.put context, :necessary_key, :necessary_value
    end

    should( "have necessary key", context ) do
      assert context.necessary_key == :necessary_value
    end
  end

  having "sometimes_necessary_key" do
    setup context do
      Dict.put context, :sometimes_necessary_key, :sometimes_necessary_value
    end

    should( "have necessary key", context ) do
      assert context.sometimes_necessary_key == :sometimes_necessary_value
    end
  end
end

This approach is much nicer than the alternatives when you're testing something like a controller with dramatically different requirements across tests:

having "a logged in user" do
  setup context do
    login context, user
  end

  ...
end

having "a logged out user" do
   ...
end

having "a logged in admin" do
  setup context do
    login context, admin
  end

  ...
end

Use assign to set the context

assign is a macro that is syntactic sugar for updating the context.

setup context do
  Dict.put context, :necessary_key, :necessary_value
end

becomes

setup context do
  assign context, necessary_key: :necessary_value
end

Use matchers simplify tests

You can package macros that write your own tests. Matchers encode common assertion patterns. For example, our plug matchers

having "a logged in admin" do
  setup context do
    login context, admin
  end

  having "a get to :index" do
    setup context do
      # process get
    end
    should_respond_with :success
    should_match_body_to "<html>"
  end
end

The two matchers, should_respond_with and should_match_body_to, will run in a single test, against the context created in the setup function (or setup functions, if you've used multiple contexts). Even if both of these tests fail, you'll see two failures in your output.

Create your own matchers with defmatcher

We come prepackaged with a set of matchers, but you can code your own as well. The following is the matcher to check for existence of a dictionary key in the context:

defmatcher should_assign_key([{key, value}]) do
  quote do
    assert var!(context)[unquote(key)] == unquote(value)
  end
end

This macro allows you to build a matcher macro.

We'll have more information about creating matchers later. In the mean time, you can read through the matchers we've created in the project. Matchers should be stateless, as all matchers within a having clause will run to completion, unless there is an error, even if a test fails.

Existing Matchers

  • Context
    • should_assign_key key, value: assert that the value for key in the context is value
    • should_match_key key, expected: assert that the value for key in the context satisfies the pattern match expected
    • should_have_key key: assert that key exists in the context
    • should_not_have_key key: assert that key does not exist in the context
  • Plug
    • should_respond_with expected: Assert that the value for context.connection.status in the context matches a reasonable value for :success, :redirect, :bad_request, :unauthorized, :missing or :error
    • should_match_body_to expected: Assert that the value for context.resp_body contains the text expected.

Unique IDs

When running tests asynchronously it can be useful to have a way to generate IDs or names that will not conflict with other tests that run concurrently. uid() will generate an ID unique for the current test and setup. If it is called again during the same test it will return the same ID. An additional string can be given uid("some string") so multiple IDs can be generated during the same test.

One Experiment, Multiple Measurements

The philosophy is that experiments go in setup and measurements go into matchers. shouldi will make sure that the context is passed between them cleanly so that things compose correctly.

When you run a shouldi test, for each context:

  • one should test is created, collecting all of the matchers in a having clause.
  • one exunit test is created for each should block
  • for each test
    • all of the ancestor setup functions will fire, from outermost to innermost.
    • the test will fire
    • if a test is a matcher test, all of the matchers will run to completion, even if there is a failure, stopping only on errors.
    • if a test is a should block, the first failure will halt the test, as in ExUnit.

Happy testing. Open an issue if there are any matchers you'd like to see. Feedback and pull requests are welcome. Send a pull request if you'd like to contribute.

Special thanks to ThoughtBot's shoulda, which formed the foundation for this approach.