ExUnit v1.9.2 ExUnit.Callbacks View Source

Defines ExUnit callbacks.

This module defines the setup/1, setup/2, setup_all/1, and setup_all/2 callbacks, as well as the on_exit/2, start_supervised/2 and stop_supervised/1 functions.

The setup callbacks are defined via macros and each one can optionally receive a map with test state and metadata, usually referred to as context. The context to be used in the tests can be optionally extended by the setup callbacks by returning a properly structured value (see below).

The setup_all callbacks are invoked only once per module, before any test is run. All setup callbacks are run before each test. No callback is run if the test case has no tests or all tests have been filtered out.

setup and setup_all callbacks can be defined by a block, by passing an atom naming a one-arity function, or by passing a list of such atoms. Both can opt to receive the current context by specifying it as parameter if defined by a block. Functions used to define a test setup must accept the context as single argument.

A test module can define multiple setup and setup_all callbacks, and they are invoked in order of appearance.

start_supervised/2 is used to start processes under a supervisor. The supervisor is linked to the current test process. The supervisor as well as all child processes are guaranteed to terminate before any on_exit/2 callback runs.

on_exit/2 callbacks are registered on demand, usually to undo an action performed by a setup callback. on_exit/2 may also take a reference, allowing the callback to be overridden in the future. A registered on_exit/2 callback will always run, while failures in setup and setup_all will stop all remaining setup callbacks from executing.

Finally, setup_all callbacks run in a separate process per module, while all setup callbacks run in the same process as the test itself. on_exit/2 callbacks always run in a separate process, as implied by their name. The test process always exits with reason :shutdown, which means any process linked to the test process will also exit, although asynchronously. Therefore it is preferred to use start_supervised/2 to guarantee synchronous termination.

Here is a rundown of the life-cycle of the test process:

  1. the test process is spawned
  2. it runs setup/2 callbacks
  3. it runs the test itself
  4. it stops all supervised processes
  5. the test process exits with reason :shutdown
  6. on_exit/2 callbacks are executed in a separate process

Context

If setup_all or setup return a keyword list, a map, or {:ok, keywords | map}, the keyword list or map will be merged into the current context and will be available in all subsequent setup_all, setup, and the test itself.

Returning :ok leaves the context unchanged (in setup and setup_all callbacks).

Returning anything else from setup_all will force all tests to fail, while a bad response from setup causes the current test to fail.

Examples

defmodule AssertionTest do
  use ExUnit.Case, async: true

  # "setup_all" is called once per module before any test runs
  setup_all do
    IO.puts("Starting AssertionTest")

    # Context is not updated here
    :ok
  end

  # "setup" is called before each test
  setup do
    IO.puts("This is a setup callback for #{inspect(self())}")

    on_exit(fn ->
      IO.puts("This is invoked once the test is done. Process: #{inspect(self())}")
    end)

    # Returns extra metadata to be merged into context
    [hello: "world"]

    # Similarly, any of the following would work:
    #   {:ok, [hello: "world"]}
    #   %{hello: "world"}
    #   {:ok, %{hello: "world"}}
  end

  # Same as above, but receives the context as argument
  setup context do
    IO.puts("Setting up: #{context.test}")
    :ok
  end

  # Setups can also invoke a local or imported function that returns a context
  setup :invoke_local_or_imported_function

  test "always pass" do
    assert true
  end

  test "uses metadata from setup", context do
    assert context[:hello] == "world"
    assert context[:from_named_setup] == true
  end

  defp invoke_local_or_imported_function(context) do
    [from_named_setup: true]
  end
end

Link to this section Summary

Functions

Defines a callback that runs once the test exits.

Defines a callback to be run before each test in a case.

Defines a callback to be run before each test in a case.

Defines a callback to be run before all tests in a case.

Defines a callback to be run before all tests in a case.

Starts a child process under the test supervisor.

Same as start_supervised/2 but returns the PID on success and raises if not started properly.

Stops a child process started via start_supervised/2.

Link to this section Functions

Link to this function

on_exit(name_or_ref \\ make_ref(), callback)

View Source
on_exit(term(), (() -> term())) :: :ok

Defines a callback that runs once the test exits.

callback is a function that receives no arguments and runs in a separate process than the caller.

on_exit/2 is usually called from setup and setup_all callbacks, often to undo the action performed during the setup. However, on_exit/2 may also be called dynamically, where a reference can be used to guarantee the callback will be invoked only once.

Defines a callback to be run before each test in a case.

Accepts a block or the name of a one-arity function in the form of an atom, or a list of such atoms.

Can return values to be merged into the context, to set up the state for tests. For more details, see the "Context" section shown above.

Examples

def clean_up_tmp_directory(context) do
  # perform setup
  :ok
end

setup :clean_up_tmp_directory

setup do
  [conn: Plug.Conn.build_conn()]
end
Link to this macro

setup(context, block)

View Source (macro)

Defines a callback to be run before each test in a case.

Accepts a block or the name of a one-arity function in the form of an atom, or a list of such atoms.

Can return values to be merged into the context, to set up the state for tests. For more details, see the "Context" section shown above.

Examples

setup context do
  [conn: Plug.Conn.build_conn()]
end
Link to this macro

setup_all(block)

View Source (macro)

Defines a callback to be run before all tests in a case.

Accepts a block or the name of a one-arity function in the form of an atom, or a list of such atoms.

Can return values to be merged into the context, to set up the state for tests. For more details, see the "Context" section shown above.

Examples

def clean_up_tmp_directory(context) do
  # perform setup
  :ok
end

# block
setup_all do
  [conn: Plug.Conn.build_conn()]
end

# one-arity function name
setup_all :clean_up_tmp_directory
Link to this macro

setup_all(context, block)

View Source (macro)

Defines a callback to be run before all tests in a case.

Accepts a block or the name of a one-arity function in the form of an atom, or a list of such atoms.

Can return values to be merged into the context, to set up the state for tests. For more details, see the "Context" section shown above.

Examples

setup_all context do
  [conn: Plug.Conn.build_conn()]
end
Link to this function

start_supervised(child_spec_or_module, opts \\ [])

View Source (since 1.5.0)
start_supervised(
  Supervisor.child_spec() | module() | {module(), term()},
  keyword()
) :: Supervisor.on_start_child()

Starts a child process under the test supervisor.

It expects a child specification or a module, similar to the ones given to Supervisor.start_link/2. For example, if your application starts a supervision tree by running:

Supervisor.start_link([MyServer, {OtherSupervisor, ...}], ...)

You can start those processes under test in isolation by running:

start_supervised(MyServer)
start_supervised({OtherSupervisor, :initial_value})

A keyword list can also be given if there is a need to change the child specification for the given child process:

start_supervised({MyServer, :initial_value}, restart: :temporary)

See the Supervisor module for a discussion on child specifications and the available specification keys.

The advantage of starting a process under the test supervisor is that it is guaranteed to exit before the next test starts. Therefore, you don't need to remove the process at the end of your tests via stop_supervised/1. You only need to use stop_supervised/1 if you want to remove a process from the supervision tree in the middle of a test, as simply shutting down the process would cause it to be restarted according to its :restart value.

This function returns {:ok, pid} in case of success, otherwise it returns {:error, reason}.

Link to this function

start_supervised!(child_spec_or_module, opts \\ [])

View Source (since 1.6.0)
start_supervised!(
  Supervisor.child_spec() | module() | {module(), term()},
  keyword()
) :: pid()

Same as start_supervised/2 but returns the PID on success and raises if not started properly.

Link to this function

stop_supervised(id)

View Source (since 1.5.0)
stop_supervised(id :: term()) :: :ok | {:error, :not_found}

Stops a child process started via start_supervised/2.

This function expects the id in the child specification. For example:

{:ok, _} = start_supervised(MyServer)
:ok = stop_supervised(MyServer)

It returns :ok if there is a supervised process with such id, {:error, :not_found} otherwise.