Myrddin: Subtests

Subtests

Often, simply running one binary per test is not sufficient. In many cases, it makes a good deal of sense to bundle a large number of tests in one binary or command. This can be because splitting each test into its own binary is clunky, or because there are simply too many processes, or simply because you don't want to test from Myrddin code -- instead, you may want to run a script.

The mbld subtest protocol is designed to accomodate these uses. If a test, of any sort, outputs data using the mtest protocol, then mbld will interpret the subtests appropriately, displaying useful output for them, and logging them at a more granular level than test binaries.

Using libtestr

Of course, writing while writing mtest output isn't difficult, it's often convenient to have a test runner library available to you, which handles the output directly. Myrddin ships with one such library for Myrddin, libtestr. It can be used as follows:

use testr

const main = {
    testr.run([
        [.name="true", .fn={ctx; 
            std.check(true, "true isn't true\n")}],
        [.name="false", .fn={ctx; 
            std.check(!false, "!false isn't true\n")}],
    ][:])
}

For more information, take a look at the testr documentation

The MTEST protocol

The mtest protocol is a simple test protocol inspired by TAP, although it is designed to solve a few problems I had with tap.

An MTEST test starts with a test plan, which looks something like this:

MTEST <ntests>

The test plan starts with the word 'MTEST' at the 0th character in the line, followed by an integer ntests representing number of tests we expect to see. If a negative number of tests is specified, then any number of tests are accepted. The number of tests is given up front in order to make it easy to detect missing tests.

This MTEST line may appear in the test output multiple times. Each time it appears, it indicates that the prevous ntests tests must have successfully completed, and that another ntest tests are expected. This allows multiple runs of tests to be emitted by the test framework, with less pain in counting them up front.

This is then followed by ntest test outputs. A test output looks like

test <name> <<{!

This specifies the test name. After this come any number of lines of log output, which may be preserved by the framework for later analysis. Finally, this is followed by the test ending:

!}>> ok

for a successful test, and

!}>> fail [reason]

for an unsuccessful test. The reason reason is shown in the mbld log output.

Writing your own provider

For Myrddin, writing a custom test provider is trivial. libtestr is the best solution, but if it's unsuitable for whatever reason, an mbld test binary is also a good solution:

test foo =
    bar.myr
;;

However, what if you want to write your own test script? This is also not difficult:

cmd my-test-cmd {test} =
    ./test.sh
;;

would suffice. Any command that mbld will run can be tagged as a test and run this way. For a working example of a custom test script, you can look in the mbld test/ drectory for the compiler tests