uncaughtException: report more than one exception per test

[juergba]

Description

describe('suite', function() {
  it('should report the first of multiple exceptions', function(done) {
    process.nextTick(() => {
      console.log('first');
      throw new Error('first');
    });
    process.nextTick(() => {
      console.log('second');
      done(new Error('second'));
    });
  });
});

The first error is not reported at all, instead the output shows two copies of the second error.

  suite
first
    1) should report the first of multiple exceptions
second
    2) should report the first of multiple exceptions

  0 passing (10ms)
  2 failing

  1) suite
       should report the first of multiple exceptions:
     Error: second
      [...]

  2) suite
       should report the first of multiple exceptions:
     Error: second
      [...]

Description of the Change

• test.err: currently is storing just one error per test, in case of multiple errors it's the last one. I haven't changed its type to Array for backwards compability and instead introduced a new property test.err.multiple to store additional errors. The latter is set within the EVENT_TEST_FAIL event handler.
• output: I applied the changes to Base.list() which is part of the epilogue used by most builtin reporters.
• Reporters as "json" or "XUnit" which don't rely on the Base#epilogue() remain mostly unchanged and do not list multiple errors per test. They list now the first error instead of the last one.

Applicable issues

#2906 partially

[coveralls]

Coverage increased (+0.02%) to 92.71% when pulling 7e2782e on juergba/uncaught-double into 2aef07d on master.

[juergba]

I'm going to merge this PR within the next few days.

[craigtaub]

LGTM