======================== Transcript based testing ======================== A transcript is both the input and output of a successful session of a ``cmd2``-based app which is saved to a text file. With no extra work on your part, your app can play back these transcripts as a unit test. Transcripts can contain regular expressions, which provide the flexibility to match responses from commands that produce dynamic or variable output. Creating a transcript ===================== Here's a transcript created from ``python examples/example.py``: .. code-block:: none (Cmd) say -r 3 Goodnight, Gracie Goodnight, Gracie Goodnight, Gracie Goodnight, Gracie (Cmd) mumble maybe we could go to lunch like maybe we ... could go to hmmm lunch (Cmd) mumble maybe we could go to lunch well maybe we could like go to er lunch right? This transcript has three commands: they are on the lines that begin with the prompt. The first command looks like this: .. code-block:: none (Cmd) say -r 3 Goodnight, Gracie Following each command is the output generated by that command. The transcript ignores all lines in the file until it reaches the first line that begins with the prompt. You can take advantage of this by using the first lines of the transcript as comments. .. code-block:: none # Lines at the beginning of the transcript that do not ; start with the prompt i.e. '(Cmd) ' are ignored. /* You can use them for comments. */ All six of these lines before the first prompt are treated as comments. (Cmd) say -r 3 Goodnight, Gracie Goodnight, Gracie Goodnight, Gracie Goodnight, Gracie (Cmd) mumble maybe we could go to lunch like maybe we ... could go to hmmm lunch (Cmd) mumble maybe we could go to lunch maybe we could like go to er lunch right? In this example I've used several different commenting styles, and even bare text. It doesn't matter what you put on those beginning lines. Everything before .. code-block:: none (Cmd) say -r 3 Goodnight, Gracie will be ignored. If we used this transcript as-is, it would likely fail. As you can see, the ``mumble`` command doesn't always return the same thing. The ``mumble`` command inserts random words into the input. Regular expressions can be included in the response portion of a transcript, and are surrounded by slashes. .. code-block:: none (Cmd) mumble maybe we could go to lunch /.*\bmaybe\b.*\bcould\b.*\blunch\b.*/ (Cmd) mumble maybe we could go to lunch /.*\bmaybe\b.*\bcould\b.*\blunch\b.*/ Without creating a tutorial on regular expressions, this one matches anything that has the words ``maybe``, ``could``, and ``lunch`` in that order. It doesn't ensure that ``we`` or ``go`` or ``to`` appear in the output, but it does work if mumble happens to add words to the beginning or the end of the output. Since the output could be multiple lines long, ``cmd2`` uses multiline regular expression matching, and also uses the ``DOTALL`` flag, which subtly changes the behavior of commonly used special characters like ``.``, ``^`` and ``$``, so you may want to double check the `Python regular expression documentation `_. You also need to be careful when using ``\Z``, it matches after the newline at the end of the string. If your output has slashes in it, you will need to escape those slashes so the stuff between them is not interpred as a regular expression. In this transcript: .. code-block:: none (Cmd) say cd /usr/local/lib/python3.6/site-packages /usr/local/lib/python3.6/site-packages the output contains slashes. The text between the first slash and the second slash, will be interpreted as a regular expression, and those two slashes will not be included in the comparison. When replayed, this transcript would therefore fail. To fix it, we could either write a regular expression to match the path instead of specifying it verbatim, or we can escape the slashes: .. code-block:: none (Cmd) say cd /usr/local/lib/python3.6/site-packages \/usr\/local\/lib\/python3.6\/site-packages .. warning:: Be aware of trailing spaces and newlines. Your commands might output trailing spaces which are impossible to see. Some terminal emulators strip trailing space when you copy text from them. This could make the actual data generated by your app different than the text you pasted into the transcript, and it might not be readily obvious why the transcript is not passing. If you aren't using regular expressions, make sure the newlines at the end of your transcript exactly match the output of your commands. A common cause of a failing transcript is an extra or missing newline. If you are using regular expressions, be aware that depending on how you write your regex, the newlines after the regex may or may not matter. Running a transcript ==================== Once you have created a transcript, it's easy to have your application play it back and check the output. From within the ``examples/`` directory: .. code-block:: none $ python example.py --test transcript_regex.txt . ---------------------------------------------------------------------- Ran 1 test in 0.013s OK The output will look familiar if you use ``unittest``, because that's exactly what happens. Each command in the transcript is run, and we ``assert`` the output matches the expected result from the transcript. .. note:: If you have set ``allow_cli_args`` to False in order to disable parsing of command line arguments at invocation, then the use of ``-t`` or ``--test`` to run transcript testing is automatically disabled. In this case, you can alternatively provide a value for the optional ``transcript_files`` when constructing the instance of your ``cmd2.Cmd`` derived class in order to cause a transcript test to run:: from cmd2 import Cmd class App(Cmd): # customized attributes and methods here if __name__ == '__main__': app = App(transcript_files=['exampleSession.txt']) app.cmdloop()