Writing TAP Tests

Introduction

    This is a guide for users of the C TAP Harness package or similar
    TAP-based test harnesses explaining how to write tests.  If your
    package uses C TAP Harness as the test suite driver, you may want to
    copy this document to an appropriate file name in your test suite as
    documentation for contributors.

About TAP

    TAP is the Test Anything Protocol, a protocol for communication
    between test cases and a test harness.  This is the protocol used by
    Perl for its internal test suite and for nearly all Perl modules,
    since it's the format used by the build tools for Perl modules to run
    tests and report their results.

    A TAP-based test suite works with a somewhat different set of
    assumptions than an xUnit test suite.  In TAP, each test case is a
    separate program.  That program, when run, must produce output in the
    following format:

        1..4
        ok 1 - the first test
        ok 2
        # a diagnostic, ignored by the harness
        not ok 3 - a failing test
        ok 4 # skip a skipped test

    The output should all go to standard output.  The first line specifies
    the number of tests to be run, and then each test produces output that
    looks like either "ok <n>" or "not ok <n>" depending on whether the
    test succeeded or failed.  Additional information about the test can
    be provided after the "ok <n>" or "not ok <n>", but is optional.
    Additional diagnostics and information can be provided in lines
    beginning with a "#".

    Processing directives are supported after the "ok <n>" or "not ok <n>"
    and start with a "#".  The main one of interest is "# skip" which says
    that the test was skipped rather than successful and optionally gives
    the reason.  Also supported is "# todo", which normally annotates a
    failing test and indicates that test is expected to fail, optionally
    providing a reason for why.

    There are three more special cases.  First, the initial line stating
    the number of tests to run, called the plan, may appear at the end of
    the output instead of the beginning.  This can be useful if the number
    of tests to run is not known in advance.  Second, a plan in the form:

        1..0 # skip entire test case skipped

    can be given instead, which indicates that this entire test case has
    been skipped (generally because it depends on facilities or optional
    configuration which is not present).  Finally, if the test case
    encounters a fatal error, it should print the text:

        Bail out!

    on standard output, optionally followed by an error message, and then
    exit.  This tells the harness that the test aborted unexpectedly.

    The exit status of a successful test case should always be 0.  The
    harness will report the test as "dubious" if all the tests appeared to
    succeed but it exited with a non-zero status.

Writing TAP Tests

  Environment

    One of the special features of C TAP Harness is the environment that
    it sets up for your test cases.  If your test program is called under
    the runtests driver, the environment variables SOURCE and BUILD will
    be set to the top of the test directory in the source tree and the top
    of the build tree, respectively.  You can use those environment
    variables to locate additional test data, programs and libraries built
    as part of your software build, and other supporting information
    needed by tests.

    The C and shell TAP libraries support a test_file_path() function,
    which looks for a file under the build tree and then under the source
    tree, using the BUILD and SOURCE environment variables, and return the
    full path to the file.  This can be used to locate supporting data
    files.

  Perl

    Since TAP is the native test framework for Perl, writing TAP tests in
    Perl is very easy and extremely well-supported.  If you've never
    written tests in Perl before, start by reading the documentation for
    Test::Tutorial and Test::Simple, which walks you through the basics,
    including the TAP output syntax.  Then, the best Perl module to use
    for serious testing is Test::More, which provides a lot of additional
    functions over Test::Simple including support for skipping tests,
    bailing out, and not planning tests in advance.  See the documentation
    of Test::More for all the details and lots of examples.

    C TAP Harness can run Perl test scripts directly and interpret the
    results correctly, and similarly the Perl Test::Harness module and
    prove command can run TAP tests written in other languages using, for
    example, the TAP library that comes with C TAP Harness.  You can, if
    you wish, use the library that comes with C TAP Harness but use prove
    instead of runtests for running the test suite.

  C

    C TAP Harness provides a basic TAP library that takes away most of the
    pain of writing TAP test cases in C.  A C test case should start with
    a call to plan(), passing in the number of tests to run.  Then, each
    test should use is_int(), is_string(), is_double(), or is_hex() as
    appropriate to compare expected and seen values, or ok() to do a
    simpler boolean test.  The is_*() functions take expected and seen
    values and then a printf-style format string explaining the test
    (which may be NULL).  ok() takes a boolean and then the printf-style
    string.

    Here's a complete example test program that uses the C TAP library:

        #include <stddef.h>
        #include <tap/basic.h>

        int
        main(void)
        {
            plan(4);

            ok(1, "the first test");
            is_int(42, 42, NULL);
            diag("a diagnostic, ignored by the harness");
            ok(0, "a failing test");
            skip("a skipped test");

            return 0;
        }

    This test program produces the output shown above in the section on
    TAP and demonstrates most of the functions.  The other functions of
    interest are sysdiag() (like diag() but adds strerror() results),
    bail() and sysbail() for fatal errors, skip_block() to skip a whole
    block of tests, and skip_all() which is called instead of plan() to
    skip an entire test case.

    The C TAP library also provides plan_lazy(), which can be called
    instead of plan().  If plan_lazy() is called, the library will keep
    track of how many test results are reported and will print out the
    plan at the end of execution of the program.  This should normally be
    avoided since the test may appear to be successful even if it exits
    prematurely, but it can make writing tests easier in some
    circumstances.

    Complete API documentation for the basic C TAP library that comes with
    C TAP Harness is available at:

        <http://www.eyrie.org/~eagle/software/c-tap-harness/>

    It's common to need additional test functions and utility functions
    for your C tests, particularly if you have to set up and tear down a
    test environment for your test programs, and it's useful to have them
    all in the libtap library so that you only have to link your test
    programs with one library.  Rather than editing tap/basic.c and
    tap/basic.h to add those additional functions, add additional *.c and
    *.h files into the tap directory with the function implementations and
    prototypes, and then add those additional objects to the library.
    That way, you can update tap/basic.c and tap/basic.h from subsequent
    releases of C TAP Harness without having to merge changes with your
    own code.

    Libraries of additional useful TAP test functions are available in
    rra-c-util at:

        <http://www.eyrie.org/~eagle/software/rra-c-util/>

    Some of the code there is particularly useful when testing programs
    that require Kerberos keys.

    If you implement new test functions that compare an expected and seen
    value, it's best to name them is_<something> and take the expected
    value, the seen value, and then a printf-style format string and
    possible arguments to match the calling convention of the functions
    provided by C TAP Harness.

  Shell

    C TAP Harness provides a library of shell functions to make it easier
    to write TAP tests in shell.  That library includes much of the same
    functionality as the C TAP library, but takes its parameters in a
    somewhat different order to make better use of shell features.

    The libtap.sh file should be installed in a directory named tap in
    your test suite area.  It can then be loaded by tests written in shell
    using the environment set up by runtests with:

        . "$SOURCE"/tap/libtap.sh

    Here is a complete test case written in shell which produces the same
    output as the TAP sample above:

        #!/bin/sh

        . "$SOURCE"/tap/libtap.sh
        cd "$BUILD"

        plan 4
        ok 'the first test' true
        ok '' [ 42 -eq 42 ]
        diag a diagnostic, ignored by the harness
        ok '' false
        skip 'a skipped test'

    The shell framework doesn't provide the is_* functions, so you'll use
    the ok function more.  It takes a string describing the text and then
    treats all of its remaining arguments as a condition, evaluated the
    same way as the arguments to the "if" statement.  If that condition
    evaluates to true, the test passes; otherwise, the test fails.

    The plan, plan_lazy, diag, and bail functions work the same as with
    the C library.  skip takes a string and skips the next test with that
    explanation.  skip_block takes a count and a string and skips that
    many tests with that explanation.  skip_all takes an optional reason
    and skips the entire test case.

    Since it's common for shell programs to want to test the output of
    commands, there's an additional function ok_program provided by the
    shell test library.  It takes the test description string, the
    expected exit status, the expected program output, and then treats the
    rest of its arguments as the program to run.  That program is run with
    standard error and standard output combined, and then its exit status
    and output are tested against the provided values.

    A utility function, strip_colon_error, is provided that runs the
    command given as its arguments and strips text following a colon and a
    space from the output (unless there is no whitespace on the line
    before the colon and the space, normally indicating a prefix of the
    program name).  This function can be used to wrap commands that are
    expected to fail with output that has a system- or locale-specific
    error message appended, such as the output of strerror().

License

    This file is part of the documentation of C TAP Harness, which can be
    found at <http://www.eyrie.org/~eagle/software/c-tap-harness/>.

    Copyright 2010 Russ Allbery <eagle@eyrie.org>

    Copying and distribution of this file, with or without modification,
    are permitted in any medium without royalty provided the copyright
    notice and this notice are preserved.  This file is offered as-is,
    without any warranty.