Capture test output and print it only for failing tests

[jarppe]

This PR captures *out*, *err*, System/out and System/err for each test thread into a ByteArrayOutputStream. The test reporter requests and prints the output for failing tests.

The implementation has a map eftest.output-capture/captured-output-contexts that is keyed by the thread id, and has the output capturing context as a value. The context has a buffer for output and a PrintWriter and PrintStream instances that both write to the buffer.

Before tests are run, the *out*, *err*, System/out and System/err are redirected to a proxied implementations of PrintWriter and PrintStream. These proxies intercept calls and redirect them to actual writer and stream found from captured-output-contexts selected by the current thread.

This allows keeping output from multiple threads separate, even with the System/out and System/err being shared by all threads.

Since the PrintStream and PrintWriter are concrete classes without suitable interfaces we can't use clojure.core/proxy. This implementation uses the javassist library for byte code generation.

The test reporter can then ask the generated output for the current thread and print it.

[Deraen]

At the least there should probably be an option to enable and disable this. Maybe :catch-output? option to run-tests?

[weavejester]

Thanks for the PR - I've added some review suggestions and questions.

[jarppe]

I reverted the version change and cleaned the set warning for reflection thing.

[jarppe]

Actually the PrintStream is not buffering the output to next OutputStream (thanks @miikka), so the solution you suggested seems to be working just fine.

I updated the PR so that the delegating proxy is created on OutputStream using clojure.lang/proxy and I dropped the dep to javassist.

Consequently the code is much shorter and simpler now.

I'm not sure how to test this, but I made a test project with lots of tests that were run in parallel, and I did not see any problems with the outputs.

[weavejester]

Looking at the source of PrintStream, it would appear that all methods write, then flush to the OutputStream within a synchronized block, which is why proxying the OutputStream is currently safe. While this may change in future (there doesn't seem to be a guarantee in the docs), it seems unlikely to, so it's probably something we can reasonably rely on.

[weavejester]

Oh, I should also add that I agree with @Deraen that there should be an option to disable this, as it might not be wanted or viable in some cases.

[weavejester]

This patch should be okay to merge, once an option is added to disable this functionality, and the commits are squashed and the commit message cleaned up.

[jarppe]

@weavejester Added option for output capture and commits squashed to one.

[weavejester]

Almost perfect. Could you make it so that :catch-out? being true is the default? I think, most of the time, catching the output is the right thing to do.

[jarppe]

The catch-out? is now true by default.

[weavejester]

Perfect, thanks!