Testing Click Applications
==========================

.. currentmodule:: click.testing

For basic testing, Click provides the :mod:`click.testing` module which
provides test functionality that helps you invoke command line
applications and check their behavior.

These tools should really only be used for testing as they change
the entire interpreter state for simplicity and are not in any way
thread-safe!

Basic Testing
-------------

The basic functionality for testing Click applications is the
:class:`CliRunner` which can invoke commands as command line scripts.  The
:meth:`CliRunner.invoke` method runs the command line script in isolation
and captures the output as both bytes and binary data.

The return value is a :class:`Result` object, which has the captured output
data, exit code, and optional exception attached.

Example::

    import click
    from click.testing import CliRunner

    def test_hello_world():
        @click.command()
        @click.argument('name')
        def hello(name):
            click.echo('Hello %s!' % name)

        runner = CliRunner()
        result = runner.invoke(hello, ['Peter'])
        assert result.exit_code == 0
        assert result.output == 'Hello Peter!\n'

File System Isolation
---------------------

For basic command line tools that want to operate with the file system, the
:meth:`CliRunner.isolated_filesystem` method comes in useful which sets up
an empty folder and changes the current working directory to.

Example::

    import click
    from click.testing import CliRunner

    def test_cat():
        @click.command()
        @click.argument('f', type=click.File())
        def cat(f):
            click.echo(f.read())

        runner = CliRunner()
        with runner.isolated_filesystem():
            with open('hello.txt') as f:
                f.write('Hello World!')

            result = runner.invoke(cat, ['hello.txt'])
            assert result.exit_code == 0
            assert result.output == 'Hello World!\n'

Input Streams
-------------

The test wrapper can also be used to provide input data for the input
stream (stdin).  This is very useful for testing prompts, for instance::

    import click
    from click.testing import CliRunner

    def test_prompts():
        @click.command()
        @click.option('--foo', prompt=True)
        def test(foo):
            click.echo('foo=%s' % foo)

        runner = CliRunner()
        result = runner.invoke(test, input='wau wau\n')
        assert not result.exception
        assert result.output == 'Foo: wau wau\nfoo=wau wau\n'

Note that prompts will be emulated so that they write the input data to
the output stream as well.  If hidden input is expected then this
obviously does not happen.