Newer versions of JUnit support concurrent test execution; however, the Spring TestContext Framework is not designed for concurrency.
The enclosed fixes sharpen focus on concurrency (including making mutable state much more distinct from immutable state), increasing separation between data for each test method run and the class they are being run on.
The patch consists of a failing test (patch 1) and a fix (patch 2), including several new tests. If you choose to apply the patch with the failing test, you must revert this before applying the fix (failing test is contained in fix patch). The included failing test may not produce concurrency issues (fail) in all cases and on all hardware platforms. They have been known to fail consistently on 3 different machines, usually upon first run.
The patch contains minor changes to the ContextLoader interface. The most significant changes have been made to the TestContextManager and TestContext classes.
Additionally upon completing the functionality, I had multiple deadlocks in the JVM when running my real test suite. I solved this by using a Java 5 ReentrantReadWriteLock in the RequestAttributes.getSessionMutex() method. It really looks to me like the creation of this mutex should be moved to one of the loader filters, since it's always created as of this patch.
Additionally, the patch contains a MockContextLoader that transfers attributes between threads. I'd really like you guys to check that code out before accepting it; there may be other smarter ways of doing this. It's only a part of the test code-base, but once it's included it sets a standard.
The patch has been applied to a local version of Spring 3 that has been running stably with multi-core machines and multi-CPU servers too. We have been running a continuous build using parallel classes, methods, and a combination of both. This is a full-scale build that was adaptable to multi-threaded test execution. The application under test uses lots of web-scopes, etc.
Parallel Test Execution
From version 3.0, Spring supports parallel test execution in the Spring TestContext Framework. Executing builds in parallel with JUnit is only supported in later versions of JUnit, and it is recommended to use at least JUnit 4.6 for this feature. Please also note that there's no guarantee your tests will run properly in parallel; a number of general concurrency issues have to be taken into account when executing tests in parallel. Your runner can usually let you choose between classes, methods, and a combination of both. Classes are usually the easiest to get working; "a combination of both" is the hardest. All three modes are supported.