WEBVTT captioned by sachac, checked by sachac
NOTE Introduction
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Hi everyone! I'm Mats Lidell.
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I'm going to talk about my journey
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writing test cases for GNU Hyperbole
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and what I learned on the way.
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So, why write tests for GNU Hyperbole?
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There is some background.
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I'm the co-maintainer of GNU Hyperbole
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together with Bob Weiner. Bob is the author of the package.
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The package is available through
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the Emacs package manager and GNU Elpa
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if you would want to try it out.
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The package has some age. I think it dates back to
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a first release around 1993, which is also
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when I got in contact with the package the first time.
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I was a user of the package for many years.
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Later, I became the maintainer of the package for the FSF.
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That was although I did not have
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much knowledge of Emacs Lisp,
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and I still have a lot to learn.
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A few years ago, we started to work actively on the package,
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with setting up goals and having meetings.
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So my starting point is that I had experience
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with test automation from development
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in C++, Java and Python
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using different x-unit frameworks like cppunit, junit.
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That was in my daytime work where
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the technique of using pull requests
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with changes backed up by tests were the daily routine.
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It was really a requirement for a change to go in
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to have supporting test cases.
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I believe, a quite common setup and requirement these days.
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I also had been an Emacs user for many years,
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but with focus on being a user.
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So as I mentioned, I have limited Emacs Lisp knowledge.
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When we decided to start
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to work actively on Hyperbole again,
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it was natural for me to look into
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raising the quality by adding unit tests.
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This also goes hand in hand
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with running these regularly as part of a build process.
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All in all, following the current best practice
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of software development.
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But since Hyperbole had no tests at all,
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it would not be enough just to add tests
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for new or changed functionality.
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We wanted to add it even broader; ideally, everywhere.
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So work started with adding tests here and there
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based on our gut feeling where it would be most useful.
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This work is still ongoing.
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So this is where my journey starts
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with much functionality to test,
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no knowledge of what testing frameworks existed,
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and not really knowing a lot about Emacs Lisp at all.
NOTE ERT: Emacs Lisp Regression Testing
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Luckily there is a package for writing tests in Emacs.
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It is called ERT: Emacs Lisp Regression Testing.
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It contains both support for defining tests and running them.
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Defining a test is done with the macro `ert-deftest`.
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In its simplest form, a test has a name, a doc string, and a body.
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The doc string is where you typically can give
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a detailed description of the test
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and has space for more info
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than what can be given in the test name.
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The body is where all the interesting things happen.
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It is here you prepare the test, run it and verify the outcome.
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Schematically, it looks like this.
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You have the ert-deftest, you have the test name,
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and the doc string, and then the body.
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It is in the body where everything interesting happens.
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The test is prepared, the function of the test is executed,
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and the outcome of the test is evaluated.
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Did the test succeed or not?
NOTE Assertions with `should`
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The verification of a test is performed with
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one or more so-called assertions.
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In ERT, they are implemented
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with the macro `should`
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together with a set of related macros.
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`should` takes a form as argument,
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and if the form evaluates to nil,
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the test has failed. So let's look at an example.
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This simple test verifies that the function `+`
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can add the numbers 2 and 3 and get the result 5.
NOTE Running a test case
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So now we have defined a test case. How do we run it?
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The ERT package has the function (or
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rather convenience alias) `ert`. It takes a test selector.
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The test name works as a selector for running just one test.
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So here we have the example. Let's evaluate it.
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We define it and then we run it using ERT.
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As you see, we get prompted for a test selector
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but we only have one test case defined at the moment.
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It's the example 0. So let's hit RET.
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As you see here, we get some output
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describing what we have just done.
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There is one test case it has passed, zero failed,
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zero skipped, total 1 of 1 test case
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and some time stamps for the execution.
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We also see this green mark here indicating one test case
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and that it was successful.
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For inspecting the test, we can hit the letter `l`
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which shows all the `should` forms
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that was executed during this test case.
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So here we see that we have the `should`,
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one `should` executed, and we see the form equals to 2,
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and it was 5 equals to 5.
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So a good example of a successful test case.
NOTE Debug a test
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So now we've seen how we can run a test case.
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Can we debug it? Yes. For debugging a test case,
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the `ert-deftest` can be set up using `edebug-defun`,
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just as a function or macro is set up
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or instrumented for debugging. So let's try that.
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So we try `edebug-defun` here.
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Now it's instrumented for debugging.
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And we run it, `ert`, and we're inside the debugger,
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and we can inspect here what's happening.
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Step through it and yes it succeeded just as before.
NOTE Commercial break: Hyperbole
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It's time for a commercial break!
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Hyperbole itself can help with running tests
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and also help with running them in debug mode.
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That is because hyperbole identifies the `ert-deftest`
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as an implicit button. An implicit button is basically
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a string or pattern
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that Hyperbole has assigned some meaning to.
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For the string `ert-deftest`, it is to run the test case.
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You activate the button with the action-key.
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The standard binding is the middle mouse button,
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or from the keyboard, M-RET.
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So let's try that.
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We move the cursor here and then we type M-RET.
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And boom, the test case was executed.
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And to run it in debug mode we type C-u M-RET
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to get the assist key, and then we're in the debugger.
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So that's pretty useful and convenient.
NOTE Instrument function on the fly
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A related useful feature here is the step-in functionality
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bound to the letter i in `debug-mode`.
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It allows you to step into a function
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and continue debugging from there.
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For the cases where your test does not do what you want,
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looking at what happens in the function of the test
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can be really useful. Let's try that with another example.
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So here we have two helper functions, one `f1-add`,
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that use the built-in `+` function
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and then we have `my-add` that uses that function.
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So we're going to test myadd.
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And then let's run this.
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Let's run this using hyperbole in debug mode
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C-u M-RET. We're in the debugger again,
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and let's step up front to my function under test
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and then press `i` for getting it instrumented
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and going into it for debugging.
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And here we can expect that it's getting
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the arguments 1 and 3,
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and it returns the result 4 as expected.
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And yes, of course, our test case will then succeed.
NOTE Mocking
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The next tool in our toolbox is mocking.
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Mocking is needed when we want to simulate the response
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from a function used by the function under test.
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That is the implementation of the function.
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This could be for various reasons.
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One example could be because it would be hard or impossible
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in the test setup to get the behavior you want to test for,
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like an external error case.
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But the mock can also be used to verify
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that the function is called with a specific argument.
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We can view it as a way to isolate the function on the test
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from its dependencies.
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So in order to test the function in isolation,
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we need to cut out any dependencies to external behavior.
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Most obvious would be dependencies to external resources,
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such as web pages. As an example:
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Hyperbole contains functionality to link you to
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social media resources and other resources on the net.
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Testing that would require the test system to call out
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to the social media resources
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and would depend on it being available, etc.
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Nothing technically stops a test case
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to depend on the external resources,
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but would, if nothing else, be flaky or slow.
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It could be part of an end-to-end suite
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where we want to test that it works all the way.
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In this case, we want to look at the isolated case
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that can be run with no dependency on external resources.
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What you want to do is to replace the function with a mock
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that behaves as the real function would do.
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The package I have found
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and have used for mocking is `el-mock`.
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The workhorse in this package is the `with-mock` macro.
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It looks like this: `with-mock` followed by a body.
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In the execution of the body, stubs and mocks
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defined in the body is respected.
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Let's look at some examples to make that clearer.
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In this case, we have the macro `with-mock`.
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It works so that the expression
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`stub + => 10` is interpreted
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so that the function `+` will be replaced with the stub.
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The stub will return 10 regardless how it is called.
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Note that the stub function
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does not have to be called at this level
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but could be called at any level in the call chain.
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By knowing how the function under test is implemented
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and how the implementation works,
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you can find function calls you want to mock
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to force certain behavior that you want to test,
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or to avoid calls to external resources, slow calls, etc.
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Simply isolate the function under test
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and simulate its environment.
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Mock is a little bit more sophisticated
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and depends on the arguments
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that the mock function is called with.
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Or more precise, it is checked
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after the `with-mock` clause
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that the arguments match the arguments it was called with
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or even if it was called at all.
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If it is called with other arguments
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there will be an error,
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and if it's not called, it is also an error.
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So this way, we are sure that the function
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we were expected to be called actually was called.
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An important piece of the testing.
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So we are sure that the mock we have provided
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actually is triggered by the test case.
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So here we have an example of `with-mock`
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where the `f1-add` function is mocked,
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so that if it's called with 2 and 3 as arguments,
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it will return 10. Then we have a test case
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where we try the `my-add` function,
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as you might remember, and call that with 2 and 3
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and see that it should also then return 10
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because it's using `f1-add`.
NOTE cl-letf
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Moving over to `cl-letf`.
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In rare occasions, the limitations of `el-mock` means
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you would want to implement a full-fledged function
00:14:50.240 --> 00:14:52.979
to be used under test.
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Then the macro `cl-letf` can be useful.
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However, you need to handle the case yourself
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if the function was not called.
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Looking through the test cases where I have used `cl-letf`,
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I think most can be implemented using plain mocking.
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Cases left is where the args to the mock might be different
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due to environment issues.
00:15:13.740 --> 00:15:24.099
In that case, a static mock will not work.
NOTE Hooks
00:15:24.100 --> 00:15:30.719
Another trick is that functions that uses hooks.
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You can overload or replace the hooks to do the testing.
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So you can use the hook function just to do the verification
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and not do anything useful in the hook.
00:15:43.120 --> 00:15:45.079
Also, here you need to be careful
00:15:45.080 --> 00:15:55.719
to make sure the test handler is called and nothing else.
NOTE Side effects and initial buffer state
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So far we have been talking about testing
00:15:57.680 --> 00:15:59.039
and what the function returns.
00:15:59.040 --> 00:16:01.119
In the best of words, we have a pure function
00:16:01.120 --> 00:16:02.959
that only depends on its arguments
00:16:02.960 --> 00:16:04.939
and produces no side effects.
00:16:04.940 --> 00:16:06.899
Many operations produce side effects
00:16:06.900 --> 00:16:09.479
or operate on the contents of buffers
00:16:09.480 --> 00:16:12.379
such as writing a message in the message buffer,
00:16:12.380 --> 00:16:15.659
change the state of a buffer, move point etc.
00:16:15.660 --> 00:16:18.859
Hyperbole is not an exception. Quite the contrary.
00:16:18.860 --> 00:16:20.839
Much of the functions creating links
00:16:20.840 --> 00:16:24.420
are just about updating buffers.
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This poses a special problem for tests.
00:16:28.560 --> 00:16:29.839
The test gets longer
00:16:29.840 --> 00:16:31.919
since you need to create buffers and files,
00:16:31.920 --> 00:16:33.279
initialize the contents.
00:16:33.280 --> 00:16:35.159
Verifying the outcome becomes trickier
00:16:35.160 --> 00:16:39.019
since you need to make sure you look at the right place.
00:16:39.020 --> 00:16:41.039
At the end of the test, you need to clean up,
00:16:41.040 --> 00:16:43.439
both for not leaving a lot of garbage
00:16:43.440 --> 00:16:45.279
in buffers and files around,
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and even worse, not cause later tests
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to depend on the leftovers from the other tests.
00:16:50.960 --> 00:16:53.079
Here are some functions and variables
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I have found useful for this.
NOTE with-temp-buffer
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For creating tests: `with-temp-buffer`:
00:17:09.200 --> 00:17:11.919
it provides you a temp buffer that you visit,
00:17:11.920 --> 00:17:13.719
and afterwards, there is no need to clean up.
00:17:13.720 --> 00:17:16.519
This is the first choice if that is all you need.
NOTE make-temp-file
00:17:16.520 --> 00:17:20.519
`make-temp-file`: If you need a file,
00:17:20.520 --> 00:17:21.959
this is the function to use.
00:17:21.960 --> 00:17:24.279
It creates a temp file or a directory.
00:17:24.280 --> 00:17:26.959
The file can be filled with initial contents.
00:17:26.960 --> 00:17:31.019
This needs to be cleaned up after a test.
00:17:31.020 --> 00:17:33.287
Moving on to verifying and debugging:
NOTE buffer-string
00:17:33.288 --> 00:17:38.247
`buffer-string`: returns the full contents
00:17:38.248 --> 00:17:39.499
of the buffer as a string.
00:17:39.500 --> 00:17:41.399
That can sound a bit voluminous,
00:17:41.400 --> 00:17:46.139
but since tests are normally small, this often works well.
00:17:46.140 --> 00:17:48.439
I have in particular found good use of comparing
00:17:48.440 --> 00:17:50.399
the contents of buffers with the empty string.
00:17:50.400 --> 00:17:53.359
That would give an error, but as we have seen
00:17:53.360 --> 00:17:56.079
with the output produced by the `should` assertion,
00:17:56.080 --> 00:17:58.079
this is almost like a print statement
00:17:58.080 --> 00:18:01.199
and can be compared with the good old technique
00:18:01.200 --> 00:18:04.399
of debugging with print statements.
00:18:04.400 --> 00:18:06.247
There might be other ways to do the same
00:18:06.248 --> 00:18:09.919
as we saw with debugging.
NOTE buffer-name
00:18:09.920 --> 00:18:13.719
buffer-name: Getting the buffer name is good
00:18:13.720 --> 00:18:16.239
to verify what buffer we are looking at.
00:18:16.240 --> 00:18:18.359
I often found it useful to check
00:18:18.360 --> 00:18:21.119
that my assumptions on what buffer I am acting on
00:18:21.120 --> 00:18:23.399
is correct by adding `should` clauses
00:18:23.400 --> 00:18:25.399
in the middle of the test execution
00:18:25.400 --> 00:18:27.399
or after preparing the test input.
00:18:27.400 --> 00:18:31.679
Sometimes Emacs can switch buffers in strange ways,
00:18:31.680 --> 00:18:34.199
maybe because the test case is badly written,
00:18:34.200 --> 00:18:37.239
and making sure your assumptions are correct
00:18:37.240 --> 00:18:40.339
is a good sanity check.
00:18:40.340 --> 00:18:42.239
Even the ert package does
00:18:42.240 --> 00:18:44.879
some buffer and windows manipulation for its reporting
00:18:44.880 --> 00:18:47.487
that I have not fully learned how to master,
00:18:47.488 --> 00:18:51.979
so assertion for checking the sanity of the test is good.
NOTE major-mode
00:18:51.980 --> 00:18:55.679
Finally, `major-mode`: Verify the buffer has the proper mode.
00:18:55.680 --> 00:19:02.679
Can also be very useful and is a good sanity check.
NOTE unwind-protect
00:19:02.680 --> 00:19:06.599
Finally, cleaning up. `unwind-protect`.
00:19:06.600 --> 00:19:09.039
The tool for cleaning up is the `unwind-protect` form
00:19:09.040 --> 00:19:12.479
which ensures that the unwind forms
00:19:12.480 --> 00:19:15.439
always are executed regardless of the outcome of the body.
00:19:15.440 --> 00:19:20.419
So if your test fails, you are sure the cleanup is executed.
00:19:20.420 --> 00:19:22.759
Let's look at unwind-protect together with
00:19:22.760 --> 00:19:30.519
the temporary file example. Many tests look like this.
00:19:30.520 --> 00:19:35.279
You create some resource, you call `unwind-protect`,
00:19:35.280 --> 00:19:42.759
you do the test, and then afterwards you do the cleanup.
00:19:42.760 --> 00:19:46.359
The cleanup for a file and a buffer is so common,
00:19:46.360 --> 00:19:50.999
so I have created a helper for that.
00:19:51.000 --> 00:19:56.559
It looks like this.
00:19:56.560 --> 00:19:59.179
The trick with the `buffer-modified` flag
00:19:59.180 --> 00:20:00.719
is to avoid getting prompted
00:20:00.720 --> 00:20:03.219
for killing a buffer that is not saved.
00:20:03.220 --> 00:20:05.439
The test buffers are often in the state
00:20:05.440 --> 00:20:15.099
where they have not been saved but modified.
NOTE Input, with-simulated-input
00:20:15.100 --> 00:20:19.679
Another problem for tests are input.
00:20:19.680 --> 00:20:21.559
In the middle of execution a function
00:20:21.560 --> 00:20:24.039
might want to have some interaction with the user.
00:20:24.040 --> 00:20:26.959
Testing this poses a problem, not only in that
00:20:26.960 --> 00:20:31.199
the input matters, but also as how even to get the test case
00:20:31.200 --> 00:20:34.079
to recognize the input!?
00:20:34.080 --> 00:20:36.039
Ideally the tests are run in batch mode,
00:20:36.040 --> 00:20:38.919
which in some sense means no user interaction.
00:20:38.920 --> 00:20:42.999
In batch mode, there is no event loop running.
00:20:43.000 --> 00:20:47.179
Fortunately, there is a package `with-simulated-input`
00:20:47.180 --> 00:20:53.259
that gets you around these issues.
00:20:53.260 --> 00:20:55.399
This is a macro that allows us
00:20:55.400 --> 00:20:56.999
to define a set of characters
00:20:57.000 --> 00:20:59.079
that will be read by the function under the test,
00:20:59.080 --> 00:21:02.579
and all of this works in batch mode. It looks like this.
00:21:02.580 --> 00:21:04.159
We have `with-simulated-input`,
00:21:04.160 --> 00:21:09.839
and then a string of characters, and then a body.
00:21:09.840 --> 00:21:11.647
The form takes a string of keys
00:21:11.648 --> 00:21:13.119
and runs the rest of the body,
00:21:13.120 --> 00:21:15.439
and if there are input required,
00:21:15.440 --> 00:21:18.119
it is picked from the string of keys.
00:21:18.120 --> 00:21:20.421
In our example, the `read-string` call
00:21:20.422 --> 00:21:21.719
will read up until RET,
00:21:21.720 --> 00:21:26.119
and then return the characters read.
00:21:26.120 --> 00:21:29.639
As you see in the example, space needs to be provided
00:21:29.640 --> 00:21:38.459
by the string SPC, as return by the string RET.
NOTE Running all tests
00:21:38.460 --> 00:21:40.799
So now we have seen ways to create test cases
00:21:40.800 --> 00:21:43.219
and even make it possible to run some of them
00:21:43.220 --> 00:21:44.679
that has I/O in batch mode.
00:21:44.680 --> 00:21:47.279
But the initial goal was to run them all at once.
00:21:47.280 --> 00:21:48.919
How do you do that?
00:21:48.920 --> 00:21:51.759
Let's go back to the `ert` command.
00:21:51.760 --> 00:21:53.799
It prompts for a test selector.
00:21:53.800 --> 00:21:56.279
If we give it the selector `t`,
00:21:56.280 --> 00:21:59.259
it will run all tests we have currently defined.
00:21:59.260 --> 00:22:05.779
Let's try that with the subset of the Hyperbole tests.
00:22:05.780 --> 00:22:09.559
Here is the test folder in the Hyperbole directory.
00:22:09.560 --> 00:22:18.819
Let's go up here and load all the demo tests.
00:22:18.820 --> 00:22:21.207
And then try to run `ert`.
00:22:21.208 --> 00:22:26.119
Now we see that we have a bunch of test cases.
00:22:26.120 --> 00:22:27.919
We can all run them individually,
00:22:27.920 --> 00:22:31.719
but we can run them with `t` instead.
00:22:31.720 --> 00:22:35.459
We will run them all at once.
00:22:35.460 --> 00:22:51.419
So now, ert is executing all our test cases.
00:22:51.420 --> 00:22:57.079
So here we have a nice green display
00:22:57.080 --> 00:23:03.219
with all the test cases.
NOTE Batch mode
00:23:03.220 --> 00:23:08.159
So that was fine, but we were still running it manually
00:23:08.160 --> 00:23:11.980
by calling ert. How could we run it from the command line?
00:23:17.180 --> 00:23:21.499
Ert comes with functions for running it in batch mode.
00:23:21.500 --> 00:23:25.639
For Hyperbole, we use `make` for repetitive tasks.
00:23:25.640 --> 00:23:27.119
So we have a make target
00:23:27.120 --> 00:23:29.279
that uses the ert batch functionality,
00:23:29.280 --> 00:23:33.259
and this is the line from the Makefile.
00:23:33.260 --> 00:23:35.479
This is a bit detailed,
00:23:35.480 --> 00:23:37.539
but you see that we have a part here
00:23:37.540 --> 00:23:40.779
where we load the test dependencies.
00:23:40.780 --> 00:23:43.520
For getting the packages
00:23:43.521 --> 00:23:48.459
such as `el-mock` and `with-simulated-input` etc. loaded.
00:23:48.460 --> 00:23:53.559
We also have... I also want to point out here the call to
00:23:53.560 --> 00:23:58.159
or the setting of `auto-save-default` to `nil`
00:23:58.160 --> 00:24:02.439
to get away with the prompt for excessive backup files
00:24:02.440 --> 00:24:05.059
that can pile up after running the tests a few times.
NOTE Skipping tests
00:24:05.060 --> 00:24:06.879
Even with the help of simulated input,
00:24:06.880 --> 00:24:08.919
not all tests can be run in batch mode.
00:24:08.920 --> 00:24:10.559
They would simply not work there
00:24:10.560 --> 00:24:12.439
and have to be run in an interactive Emacs
00:24:12.440 --> 00:24:14.179
with the running event loop.
00:24:14.180 --> 00:24:17.919
One trick still to be able to use batch mode for automation
00:24:17.920 --> 00:24:20.319
is to put the guard at the top of each test case
00:24:20.320 --> 00:24:22.559
as the first thing to be executed,
00:24:22.560 --> 00:24:25.719
so that it kicks in before anything else and stops Emacs
00:24:25.720 --> 00:24:27.199
to try to run the test case.
00:24:27.200 --> 00:24:35.519
Now, it looks like this: `(skip-unless (not noninteractive))`.
00:24:35.520 --> 00:24:38.639
So when ert sees that the test should be skipped, it skips it
00:24:38.640 --> 00:24:40.439
and makes a note of that,
00:24:40.440 --> 00:24:44.579
so you will see how many tests that have been skipped.
00:24:44.580 --> 00:24:47.559
Too bad. We have a number of test cases defined,
00:24:47.560 --> 00:24:51.359
and to run them, we need to run them manually. Well sort of.
00:24:51.360 --> 00:24:53.807
Not being able to run all tests easily
00:24:53.808 --> 00:24:58.419
is a bit counterproductive
00:24:58.420 --> 00:25:00.999
since our goal is to run all tests.
00:25:01.000 --> 00:25:04.719
There is however no ert function to run tests in batch mode
00:25:04.720 --> 00:25:06.779
with an interactive Emacs.
00:25:06.780 --> 00:25:08.479
The closest I have got is either
00:25:08.480 --> 00:25:10.079
to start the Emacs from the command line
00:25:10.080 --> 00:25:12.439
calling the ert function as we just have seen,
00:25:12.440 --> 00:25:14.799
and then killing it manually when done;
00:25:14.800 --> 00:25:19.599
or add a function to extract the contents of the ERT buffer
00:25:19.600 --> 00:25:24.599
when done and echo it to standard output.
00:25:24.600 --> 00:25:27.800
This is how it looks in the Makefile
00:25:27.801 --> 00:25:31.207
to get the behavior of cutting and paste,
00:25:31.208 --> 00:25:34.580
getting the ERT output into a file
00:25:34.581 --> 00:25:36.239
so we can then kill Emacs
00:25:36.240 --> 00:25:44.799
and spit out the content of the ERT buffer.
00:25:44.800 --> 00:25:47.739
One final word here is that
00:25:47.740 --> 00:25:54.559
when you run this in a continuous integration pipeline,
00:25:54.560 --> 00:25:59.399
you might not have a TTY for getting Emacs to start,
00:25:59.400 --> 00:26:03.200
and that is then another problem
00:26:03.201 --> 00:26:05.160
with getting the interactive mode.
NOTE Conclusion
00:26:08.460 --> 00:26:11.120
We have reached the end of the talk.
00:26:11.121 --> 00:26:14.159
If you have any new ideas
00:26:14.160 --> 00:26:16.759
or have some suggestions for improvements,
00:26:16.760 --> 00:26:18.239
feel free to reach out
00:26:18.240 --> 00:26:21.100
because I am still on the learning curve of writing,
00:26:21.101 --> 00:26:25.299
how to write good test cases.
00:26:25.300 --> 00:26:27.639
If you look at the test cases we have in Hyperbole
00:26:27.640 --> 00:26:29.799
and you think they might contradict what I am saying here,
00:26:29.800 --> 00:26:32.579
it is OK. It is probably right.
00:26:32.580 --> 00:26:34.599
I have changed the style as I go
00:26:34.600 --> 00:26:36.639
and we have not yet refactored all tests
00:26:36.640 --> 00:26:38.579
to benefit from new designs.
00:26:38.580 --> 00:26:40.599
That is also the beauty of the test case.
00:26:40.600 --> 00:26:43.319
As long as it serves its purpose, it is not terrible
00:26:43.320 --> 00:26:47.799
if it is not optimal or not having the best style.
00:26:47.800 --> 00:26:55.240
And yes, thanks for listening. Bye.
