PyTest and Flake8 outputs not always visible in console

[ameliedagenais]

Problem Sometimes the pytest or flake8 tasks fail with no output visible in the console, making it very hard to investigate issues.

Repro Steps

1. From the example-project provided in this repo, I added a few dummy tests
2. Run gradle pytest --info
3. Observe output, it will inconsistently return one or the other:

Expected:

> Task :pytest 
Task ':pytest' is not up-to-date because:
  Task has not declared any outputs.
Starting process 'command 'C:\hack\example-project\build\venv\Scripts\python.exe''. Working directory: C:\hack\example-project Command: C:\hack\example-project\build\venv\Scripts\python.exe C:\hack\example-project\build\venv\Scripts\py.test.exe C:\hack\example-project\test
Successfully started process 'command 'C:\hack\example-project\build\venv\Scripts\python.exe''
============================= test session starts =============================
platform win32 -- Python 2.7.2, pytest-3.1.2, py-1.4.34, pluggy-0.4.0
rootdir: C:\hack\example-project, inifile:
plugins: xdist-1.17.1, cov-2.5.1
collected 2 items

test\test_example.py ..

========================== 2 passed in 0.04 seconds ===========================

:pytest (Thread[Task worker for ':',5,main]) completed. Took 0.745 secs.

Actual:

Task ':pytest' is not up-to-date because:
  Task has not declared any outputs.
Starting process 'command 'C:\hack\example-project\build\venv\Scripts\python.exe''. Working directory: C:\hack\example-project Command: C:\hack\example-project\build\venv\Scripts\python.exe C:\hack\example-project\build\venv\Scripts\py.test.exe C:\hack\example-project\test
Successfully started process 'command 'C:\hack\example-project\build\venv\Scripts\python.exe''
:pytest (Thread[Task worker for ':',5,main]) completed. Took 0.773 secs.

Additionnal Info The issue is probably that the buffered output is not flushed before the process ends. I have tried to work around the problem on our side by running the pytest task with PYTHONUNBUFFERED (-u) but didn't see any improvement.

Then, as I was investigating the issue, I've been able to get stdout to print consistently with this sample task:

task myTestTask(type:Exec) {
    workingDir = project.rootDir
    if(os.isWindows()) {
        commandLine "${project.buildDir}\\venv\\Scripts\\python.exe", "${project.buildDir}\\venv\\Scripts\\py.test.exe", "${project.rootDir}\\test"
    }
    else {
        commandLine "${project.buildDir}/venv/bin/python", "${project.buildDir}/venv/bin/py.test", "${project.rootDir}/test"
    }
    standardOutput = new ByteArrayOutputStream();
    doLast {
        logger.info(standardOutput.toString())
    }
}

Capturing stdout and logging it explicitly in a doLast block was key to success and I'm hoping you guys could fix the pytest and flake8 tasks similarly within PyGradle.

Note that you would need to fix it for both stdout and stderr.