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Having a thorough test suite is something very important which is usually overlooked. It is an incredible help in preventing regression bugs and quickly assess the status of old code. For example, many packages in Octave Forge become deprecated after losing their maintainer simply because they have no test suite.

GNU Octave has multiple tools that help in creating a comprehensive test suite, accessible to both developers and end-users, as detailed on the Octave manual. Basically, test blocks are %!test comment blocks, typically at the end of a source file, which are ignored by the Octave interpreter and only read by the test function.

Running tests

To run all the tests of a specific function, simply use the test command at the Octave prompt. For example, to run the tests in mean():

octave-cli-3.8.2> test mean
PASSES 17 out of 17 tests

These tests are written in the Octave language at the bottom of the m file which defines mean(). It is important that these tests are also available for the end users so they can test the status of their installation. The whole Octave test suite can be ran with:

octave-cli-3.8.2> __run_test_suite__

Integrated test scripts:



  PASS     11556
  FAIL         3
  XFAIL        6
  SKIPPED     38

See the file test/fntests.log for additional details.

To run tests in a specific file, one can simply specify the path instead of a function name:

 test /full/path/to/file.cc

Writing tests

Tests appear as %! blocks at the bottom of the source file, together with %!demo blocks. A typical m function file, will have the following structure:

## Copyright
## A block with the copyright notice

## -*- texinfo -*-
## A block with the help text

function [x, y, z] = foo (bar)
  ## here's some amazing code

%!assert (foo (1))
%!assert (foo (1:10))
%!assert (foo ("on"), "off")
%!error <must be positive integer> foo (-1)
%!error <must be positive integer> foo (1.5)

%! ## see how cool foo() is:
%! foo([1:100])

Tests can be added to oct functions in the C++ sources just as easily, see find.cc for example. The syntax is exactly the same, but done within C comment blocks. During installation, these lines are automatically extracted from the sources and special test scripts are generated. A typical C++ source file has the following structure:

// Copyright
// A block with the copyright notice

DEFUN_DLD (foo, args, ,
"-*- texinfo -*-\n\
A block with the help text")
 \\ here's some amazing code
function [x, y, z] = foo (bar)
  ## here's some amazing code

%!assert (foo (1))
%!assert (foo (1:10))
%!assert (foo ("on"), "off")
%!error <must be positive integer> foo (-1)
%!error <must be positive integer> foo (1.5)


%!assert lines are simplest tests to write and also the most common:

%!assert (foo (bar))      # test fails if "foo (bar)" returns false
%!assert (foo (bar), qux) # test fails if "foo (bar)" is different from "qux

These are actually a shorthand version of %!test assert (foo (bar)), and assert is simply an Octave function that throws errors when two arguments fail to compare.


While single line %!asserts are the most common test used, %!test blocks are the ultimate, most useful, and flexible. The code within such block is simply processed through the Octave interpreter and if the code generates an error, then the test is said to fail. These often end with a call to assert:

%! a = [0 1 0 0 3 0 0 5 0 2 1];
%! b = [2 5 8 10 11];
%! for i = 1:5
%!   assert (find (a, i), b(1:i))
%! endfor

Test for no failure

In a few cases, there is the situation where a function returns nothing, and the only thing to test is that it causes no error. This can be tested simply with:

%!test foo (bar)


It is also important to test that a function performs its checks correctly and throws errors when it receives garbage. This can be done with error blocks:

%!error foo ()  # test that causes any error
%!error <BAR must be a positive integer> foo (-1.5)  # test that throws specific error

Shared functions

It is often useful to share a function between multiple test. Sometimes these are only small helper functions, but more often these are just simpler low performance implementations of the function being tested. These are created in %!function blocks:

%!function x = slow_foo (bar)
%!  ## a simple implementation of foo, definitely correct, but
%!  ## unfortunately too slow for anything other than tests.

%!assert (foo (bar), slow_foo (bar))

%! for i = -100:100
%!   bar = qux (i);
%!   assert (foo (bar), slow_foo (bar))
%! endfor

Code coverage