Features

• API documentation: http://erlymock-site.sourceforge.net/edoc/index.html
• battle proven in at least three large projects at http://www.lindenbaum.eu
• comprehensive runtime messages
• two-letter module name(we went from 'mock' to 'em', which was quite an improvement for us)
• small, flexible and easy to use API
• allows strict expectations
• allows stub behavior definitions to be intuitively mixed with strict expectations
• correctly restores cover compiled module
• automatic cleanup when mock or test process dies
• implemented with OTP standard behaviour
• because it is a maven project can be automatically installed as maven test dependency Please refer to the excellent maven-erlang-plugin (excellent since Version 2.0.0-SNAPSHOT) found here: http://erlang-plugin.sourceforge.net.

Usage Example

Assume there are two modules, used by the code to be tested, that shall be mocked (at least to prevent damaging side effects):

A rocket launcher server:

-module(rocket_launcher).

launch(Longitude, Latitude, Type) ->
 ....

And A UI module:

-module(rocket_launcher_ui).

ask_for_instructions() ->
 ...

Then this is how a happy case unit test might look like:

launche_missle_test() ->
   % create a new mock process
   M = em:new(),

   % define the expectations 
   em:strict(M, rocket_launcher_ui, ask_for_instructions, [], 
            {return, [{longitude, 123},
                      {latitude, 999},
                      {type, some_rocket_type}]}),
   em:strict(M, missle_lauchner, launch, [123, 999, some_rocket_type]),
  
   % tell the mock that all expectations are defined 
   em:replay(M),

   % run code under test
   rocket_app:interactive(),

   % verify expectations
   em:verify(M).

Installation und usage with Maven

Assume there is a new Project, that needs some unit testing with mocks. This is simple when using maven.

Assume there is already one source file called "borg.erl".

1. decide upon a short project name that would be a valid erlang atom without ' i.e. myproject

2. Create a directory by that name: mkdir myproject

3. Create a new maven project by writing a simple pom.xml which contains erlymock as dependency:

<project>
  <modelVersion>4.0.0</modelVersion>
  <groupId>your.group.id</groupId>
  <artifactId>myproject</artifactId>
  <version>1.0.0-SNAPSHOT</version>
  <packaging>erlang-std</packaging>
  <name>MyProject</name>
  <description>Look ma' my project!</description>
  <build>
    <plugins>
      <plugin>
        <groupId>eu.lindenbaum</groupId>
        <artifactId>maven-erlang-plugin</artifactId>
        <version>2.0.0</version>
        <extensions>true</extensions>
      </plugin>
    </plugins>
  </build>
  <dependencies>
    <dependency>
      <groupId>com.github.sheyll</groupId>
      <artifactId>em</artifactId>
      <version>3.0.0</version>
      <type>erlang-std</type>
      <scope>test</scope>
    </dependency>
  </dependencies>
</project>

4. all necessary directories by running: "mvn erlang:setup"

5. copy sources to myproject/src/

6. copy unit tests into myproject/test_src/

Now you can run 'mvn test' to run eunit. Erlymock will automatically be downloaded by maven.

History of ErlyMock

ErlyMock has undergone many stages and years of development and usage before reaching this stage. It was first published here: http://sheyll.blogspot.com/2009/02/erlang-mock-erlymock.html Then Samual Rivas cleaned it up and added support for restoring cover compiled modules for his project, see http://www.lambdastream.com/. The code was then added with all modifications to the great new erlang-maven-plugin forge which can be found here: http://sourceforge.net/projects/erlang-plugin/.

Then I decided to partially rewrite ErlyMock in order to provide a simpler API and in order to improve the code quality. Also, I wanted to use the gen_fsm OTP standard behavior.