There are ways to connect to the `rostest`'s [[roscore]], which is restarted for each test in order to have a clean test fixture.  

== Indigo and later ==

By default rostest uses a random port so many `rostest`s can be run in parallel.

=== Re-use an already-running master ===

This behavior can be overridden with the reuse-master flag, and then the standard ROS_MASTER_URI will be used for the test.

Start a roscore in another terminal, then:

{{{
rostest --reuse-master foo_package foo.test
}}}

See also [[http://answers.ros.org/question/208361/port-to-connect-to-rostest-rosmaster-after-indigo/|this question thread]] and [[https://github.com/ros/ros_comm/pull/637|this pull request]].

=== Connect to rostest's master ===

Bit hacky but it's possible. While `rostest` is running, run a command something like:
{{{
grep -r "Registering with master node" ~/.ros/log/latest
}}}

This will return the master's URL with the port number. Then update your `ROS_MASTER_URI`:
{{{
export ROS_MASTER_URI=http://localhost:%PORTNUMBER_YOUFOUND%
}}}

NOTE: Again, port number differs per every `rostest` run. When you're running `rostest` by integrated way (e.g. [[http://docs.ros.org/indigo/api/catkin/html/howto/format2/run_tests.html|catkin_make run_tests]]), multiple `rostest`s can be included and running at the same time, so that you might see multiple different port numbers in the `grep` result above. Choose the one you want to connect to carefully.

== Pre-Indigo ==

In hydro and earlier `rostest` uses port 22422 to not conflict with any running [[roscore]] instance.  Thus, to connect to the `rostest` [[Master]] from another terminal you must first:

{{{
export ROS_MASTER_URI=http://localhost:22422
}}}

== Tests without rostest ==

A different approach to connecting to the volatile [[rostest]] roscore is to run your test file using [[roslaunch]].  The <test...> portions of the test file will not run, so you then manually launch your test node to observe its behavior.  For example if the foo.test consisted of the following:

{{{
<launch>
  <node name="foo_node" pkg="foo_package" type="foo_node"
      output="screen">
  </node>
  <test test-name="foo_node-test" pkg="foo_package" type="foo_node-test" />
</launch>
}}}

Launch the node and the test separately:

{{{
roslaunch foo_package foo.test
}}}

Then in another terminal:

{{{
rosrun foo_package foo_node-test
}}}