Executing tests in parallel would be impaired by synchronized block in Spectrum

[ashleyfrieze]

In a situation where something like JUnit's ParallelComputer were used, or where other test runners were parallelising the construction of test classes run with the Spectrum runner, the fact that the test class construction happens inside a synchronized block will constrain the execution time.

This is relatively easy to fix. It's in a synchronized block to protect a stack from being bombarded by different threads. By introducing a thread-independent singleton into the mix, this will become thread-safe. This is what I propose to do.

[ashleyfrieze]

@greghaskins - this was resolved by #77

[ashleyfrieze]

I'm going to close this, since it's a detail, rather than an issue.