  ------
  Developing Surefire
  ------
  Kristian Rosenvold
  ------
 2011-03-07
  ------
  
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Developer Center

  When working with Surefire, it is necessary to understand a few things:

* Multi-module Project

  The plugin is built as part of a multi-module plugin. You need to check out 
  the complete module and build from there:

+---+
  git clone https://gitbox.apache.org/repos/asf/maven-surefire.git
+---+

* Making Test Cases for Demonstrating Problems

  When reporting an issue, it is immensely useful to create a small sample project
  that demonstrates the problem. Surefire already contains a large number of such
  projects, and they can be found at
  {{surefire-its/src/test/resources/}}.
  Typically you can check out one of the pre-existing projects and run it like this:

+---+
  cd surefire-its/src/test/resources/failsafe-buildfail
  mvn -Dsurefire.version=2.12 verify
+---+

* Attaching a Debugger

  Sometimes it's appropriate to attach a remote debugger to the Surefire fork to try to determine what
  is <really> going on. If you checkout and build trunk, you'd usually do something like this:

+---+
  mvn -Dmaven.surefire.debug=true install
+---+

  Load the source in your IDE, set a breakpoint at the start of <<<ForkedBooter#main>>> and attach
  a debugger to port 5005.

* Tracing a Forked Execution

  The forked Surefire process uses standard input and output to communicate back to the source. Sometimes when tracking troubles
  it can be helpful to look at just the output of the fork.

  This can be done by running:

+---+
mvn -e -X install | grep Forking
+---+

  If you copy the command part of the output, you should be able to re-run the command by just pasting it on
  the command line (you might have to do only the bits after <<<&&>>>).

  You can now paste this command on the command line and capture the output of the fork. This may help you
  determine if the problem is in the forked end or the receiving end.

  When investigating a particular class, you probably want to <<<grep>>> the output for the class name.
  Additionally the booter code (first field) can be seen at
  {{https://git-wip-us.apache.org/repos/asf?p=maven-surefire.git;a=blob;f=surefire-api/src/main/java/org/apache/maven/surefire/booter/ForkingRunListener.java}}

  The second field in the output (after the booter code) is the logical channel number, where different threads in the fork
  should come in different channels.

* Test Cases

  All patches to Surefire must contain test coverage, either as an integration test
  or a unit test. All new features (changed/added plugin options) must be covered by
  an end-to-end integration test.

  There are
  numerous other integration tests that all operate on small sample projects in
  <<<surefire-its/src/test/resources>>>.

  Example integration tests are <<<Surefire141PluggableProvidersIT>>> and the corresponding
  <<<surefire-its/src/test/resources/surefire-141-pluggableproviders>>>.

* Essential Source Code Reading List

  Some methods/classes reveal more about the basic working of a piece of code than others. The following classes/methods
  are a "reading list" for getting quickly acquainted with the code:

+---+
AbstractSurefireMojo#executeAllProviders
ForkStarter#fork
ForkedBooter#main
+---+

* JDK Versions

  The surefire booter is capable of booting all the way back to jdk1.8. Specifically
  this means <<<surefire-api>>>, <<<surefire-booter>>>, <<<common-junit3>>>, <<<surefire-junit3>>>
  and other modules are compiled with source/target 1.8.

* Provider Isolation

  Classes in the SUT (<Subject Under Test>) override any classes within the
  Surefire providers. This means providers using any
  third party dependencies (other than the test framework itself) should
  shade these classes to a different package.

* Common Provider Modules

  The <<<surefire-providers>>> module contains <<<common-junitXX>>> modules. These modules
  depend on the <<<XX>>> version of JUnit and can access the JUnit APIs at the correct
  JUnit version level. Unit tests can also be written that will run with the
  correct JUnit version. At build time, all of the relevant parts of these "common"
  modules are just shaded into the provider jar files.

* Shadefire

  "Shadefire" is the first module to be run in the
  Surefire build. This creates a shaded version of the JUnit provider, and this provider
  is thereafter used to build Surefire itself. This is
  because the SUT overrides the provider, and the Shadefire provider has been
  relocated to avoid this overriding when Surefire is building itself.

