package ounit2

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Unit test building blocks (v2).

  • author Sylvain Le Gall


type test_ctxt = OUnitTest.ctxt

Context of a test.

type test_fun = test_ctxt -> unit

The type of test function.

type test = OUnitTest.test

The type of test.

type test_length = OUnitTest.test_length

The expected length of the test.


Assertions are the basic building blocks of unittests.

val assert_failure : string -> 'a

Signals a failure. This will raise an exception with the specified string.

  • raises Failure

    signal a failure

val assert_bool : string -> bool -> unit

Signals a failure when bool is false. The string identifies the failure.

  • raises Failure

    signal a failure

val assert_string : string -> unit

Signals a failure when the string is non-empty. The string identifies the failure.

  • raises Failure

    signal a failure

val assert_command : ?exit_code:Unix.process_status -> ?sinput:char Seq.t -> ?foutput:(char Seq.t -> unit) -> ?use_stderr:bool -> ?backtrace:bool -> ?chdir:string -> ?env:string array -> ctxt:test_ctxt -> string -> string list -> unit

assert_command prg args Run the command provided.

  • parameter exit_code

    expected exit code

  • parameter sinput

    provide this char Seq.t as input of the process

  • parameter foutput

    run this function on output, it can contains an assert_equal to check it

  • parameter use_stderr

    redirect stderr to stdout

  • parameter backtrace


  • parameter chdir

    Chdir into a directory before running the command.

  • parameter env

    Unix environment

  • parameter verbose

    if a failed, dump stdout/stderr of the process to stderr

val assert_equal : ?ctxt:test_ctxt -> ?cmp:('a -> 'a -> bool) -> ?printer:('a -> string) -> ?pp_diff:(Format.formatter -> ('a * 'a) -> unit) -> ?msg:string -> 'a -> 'a -> unit

assert_equal expected real Compares two values, when they are not equal a failure is signaled.

  • parameter cmp

    customize function to compare, default is =

  • parameter printer

    value printer, don't print value otherwise

  • parameter pp_diff

    if not equal, ask a custom display of the difference using diff fmt exp real where fmt is the formatter to use

  • parameter msg

    custom message to identify the failure

  • parameter ctxt

    if provided, always print expected and real value

  • raises Failure

    signal a failure

val assert_raises : ?msg:string -> exn -> (unit -> 'a) -> unit

Asserts if the expected exception was raised.

  • parameter msg

    identify the failure

  • raises Failure


Skipping tests

In certain condition test can be written but there is no point running it, because they are not significant (missing OS features for example). In this case this is not a failure nor a success. Following functions allow you to escape test, just as assertion but without the same error status.

A test skipped is counted as success. A test todo is counted as failure.

val skip_if : bool -> string -> unit

skip cond msg If cond is true, skip the test for the reason explain in msg. For example skip_if (Sys.os_type = "Win32") "Test a doesn't run on windows".

val todo : string -> unit

The associated test is still to be done, for the reason given.

Compare Functions

val cmp_float : ?epsilon:float -> float -> float -> bool

Compare floats up to a given relative error.

In keeping with standard floating point semantics, NaN is not equal to anything: cmp_float nan nan = false.

  • parameter epsilon

    if the difference is smaller epsilon values are equal


A bracket is a registered object with setUp and tearDown in unit tests. Data generated during the setUp will be automatically tearDown when the test ends.

val bracket : (test_ctxt -> 'a) -> ('a -> test_ctxt -> unit) -> test_ctxt -> 'a

bracket set_up tear_down test_ctxt set up an object and register it to be tore down in test_ctxt.

val bracket_tmpfile : ?prefix:string -> ?suffix:string -> ?mode:Pervasives.open_flag list -> test_ctxt -> string * Pervasives.out_channel

bracket_tmpfile test_ctxt Create a temporary filename and matching output channel. The temporary file is removed after the test.

  • parameter prefix

    see Filename.open_temp_file

  • parameter suffix

    see Filename.open_temp_file

  • parameter mode

    see Filename.open_temp_file

val bracket_tmpdir : ?prefix:string -> ?suffix:string -> test_ctxt -> string

bracket_tmpdir test_ctxt Create a temporary dirname. The temporary directory is removed after the test.

  • parameter prefix

    see Filename.open_temp_file

  • parameter suffix

    see Filename.open_temp_file

val with_bracket_chdir : test_ctxt -> string -> (test_ctxt -> 'a) -> 'a

with_bracket_chdir test_ctxt dn f change directory to dn during execution of function f. In order to Sys.chdir, we need to take a lock to avoid other tests trying to do change the current directory at the same time. So this bracket is not directly accessible in order to use it only on shorter piece of code.

Constructing Tests

val (>:) : string -> test -> test

Create a TestLabel for a test

val (>::) : string -> test_fun -> test

Create a TestLabel for a TestCase

val (>:::) : string -> test list -> test

Create a TestLabel for a TestList

val test_case : ?length:test_length -> test_fun -> test

Generic function to create a test case.

val test_list : test list -> test

Generic function to create a test list.

Some shorthands which allows easy test construction.


  • "test1" >: TestCase((fun _ -> ())) => TestLabel("test2", TestCase((fun _ -> ())))
  • "test2" >:: (fun _ -> ()) => TestLabel("test2", TestCase((fun _ -> ())))
  • "test-suite" >::: ["test2" >:: (fun _ -> ());] => TestLabel("test-suite", TestSuite([TestLabel("test2", TestCase((fun _ -> ())))]))

Performing Tests

type log_severity = [
  1. | `Error
  2. | `Warning
  3. | `Info

Severity level for log.

val logf : test_ctxt -> log_severity -> ('a, unit, string, unit) Pervasives.format4 -> 'a

Log into OUnit logging system.

val in_testdata_dir : test_ctxt -> string list -> string

Build a filename for a file that should be located in the test data dir.

The test data dir, can be defined on the command line (preferably absolute) The default option is to locate it in topsrcdir/test/data.

val non_fatal : test_ctxt -> (test_ctxt -> unit) -> unit

non_fatal ctxt f Run f but if an exception is raised or an assert fails, don't stop, just register the result. The global test running result will mix in the non fatal result to determine the success or failure of the test.

module Conf : sig ... end

Define command line options, environment variables and file configuration.

val run_test_tt_main : ?exit:(int -> unit) -> test -> unit

Main version of the text based test runner. It reads the supplied command line arguments to set the verbose level and limit the number of test to run.

  • parameter test

    the test suite to run.


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