Add Junit report

[nirtal85]

Hi,
please add a junit report option,
as a flag to the run:
should be like bats (test files/folder) --junit

[jasonkarns]

TAP is a very common, cross-language test output format. Due to being a pseudo lingua-franca of test report outputs, there are dozens of converters from TAP to other formats. Simply piping the TAP output to other formats will get you junit output without any modification to bats.

For instance: https://github.com/aghassemi/tap-xunit via bin/bats --tap test | tap-xunit would generate xunit output.

As it stands, the current formatter could be shipped as a standalone TAP converter that just receives Bats' TAP output. Creating a separate bats-xunit project would be a fine repo for future inclusion in a potential bats-core github org. I just don't think it should necessarily be bundled within bats itself.

related upstream issue: sstephenson/bats#161

[DarwinJS]

We use Gitlab CI and it has recently gained JUNIT test results import and display - but this is the only format it supports so far. (https://gitlab.com/gitlab-org/gitlab-ce/issues/17081)

Very interested in following where this goes.

[filmil]

I think it's valuable to produce jUnit output right here in bats:

• tap format does not allow reporting test runtimes.
• the converter at https://github.com/aghassemi/tap-xunit is broken. It generates files that don't validate against the junit XSD. For example, it omits time attribute,which is required: https://github.com/windyroad/JUnit-Schema/blob/master/JUnit.xsd#L127