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Sample program that uses eunit to test a function.
-module(power).
-export([pow/2, start/0]).
-include_lib("../../lib/eunit/include/eunit.hrl").
% adjust your own path
pow(_,0) -> 1;
pow(X,1) -> X;
pow(X,N) when N>1, is_integer(N) ->
X * pow(X,N-1).
start() ->
io:format(" This is a demo for eunit, the unit testing module.\n"),
io:format(" Now testing the pow() function with eunit\n"),
io:format(" Running: eunit:test(pow)~n"),
eunit:test(pow).
power_test_() ->
[?_assert(pow(0,0) == 1),
?_assert(pow(1,1) == 1),
?_assert(pow(2,2) == 4),
?_assert(pow(3,3) == 27),
?_assert(pow(4,4) == 256),
?_assertException(error, function_clause, pow(-1,0.5))
].
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Note: Default unit test functions are automatically exported by eunit
%
% To test function power() we compile and test.
%
% 2> c(power).
% 3> eunit:test(pow).
% All 6 tests successful.
% But how does it work?
% eunit:test(pow) uses power:power_test_() to produce
% a list of 6 test functions(a test suite):
% 7> power:pow_test_().
% {15,#Fun<pow.1.106864721>},
% {16,#Fun<pow.2.81990874>},
% {17,#Fun<pow.3.122231603>},
% {18,#Fun<pow.4.90957845>},
% {19,#Fun<pow.5.90843223>},
% {20,#Fun<pow.4.90457845>}]
%
% eunit:test then runs the programs in the test suite
% and reports the results.
%
% Note: The numbers [15,16,17,18,19,20] are
% the line numbers of the source code that generated the
% test functions.
%
% Assertions
%
% Six total tests are run. An assertion is a positive assertion
% and expects the answer to be true. There are 5 positive assertions
% and 1 negative assertion in the test suite.
%
% Negative assertions
%
% A negative assertion is where an error is expected.
% If an error is generated, then the test succeeds.
% Since this power function does not know how to do
% negative bases, then it causes an error. Since an
% error is expected, the test succeeds.
%
% assertException(error, function_clause, pow(-1,0.5))
%
% is an example of a negative assertion.
% An error generates an exception. An exception is
% is a type of high level error message.
%
% See Exceptions
% for more details.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Unit tests as internal documentation
Unit tests provide a useful method of internal documentation that is
often easy to maintain. The maintenance of documentation can often
be a problem as programs evolve over time.
As long as the unit test works, the unit test serves as a nice suite
of example programs that can aid comprehension. For the purpose of
internal documentation and other reasons at least one
negative assertion is included to form a complete test suite.
A negative assertion can show the limits of
the domain or the range of a function, or even its time complexity
if one includes a timeout bound on computation time.
Software engineering
Unit tests can help one keep an eye on side-effects during
program development. Fixing a bug for some input may cause a
bug with some previously working input. Unit testing can help
with the organization of a program and inspire new solutions.
Note: for the program to work you will need to install
and perhaps compile the eunit module, and set up your path
to include it.
