Combine multiple pytest runs into one XML.

MultiRunXML

from _pytest.junitxml import LogXML, Junit
from io import open
import pytest
import sys
import time


class MultiRunXml(LogXML):
    """
    This is a wrapper around Pytest's LogXML, which
    dumps the pytest run data to XML format.

    All this does is keep track of all of the data from any test run, but only dumps
    the Test Suite when you SPECIFICALLY call dump.
    """
    
    def pytest_sessionfinish(self):
        """
        Do nothing! Overrides the base class, which would
        dump the data to XML.

        :return:
        """
        pass

    def dump(self):
        """
        Dumps all the test data to the specified XML file.

        :return:
        """
        with open(self.logfile, 'w', encoding='utf-8') as logfile:
            suite_stop_time = time.time()
            suite_time_delta = suite_stop_time - self.suite_start_time
            numtests = self.passed + self.failed

            logfile.write(u'<?xml version="1.0" encoding="utf-8"?>')
            logfile.write(Junit.testsuite(
                self.tests,
                name="pytest",
                errors=self.errors,
                failures=self.failed,
                skips=self.skipped,
                tests=numtests,
                time="%.3f" % suite_time_delta,
            ).unicode(indent=0))
            
            
  if __name__ == '__main__':
    arg_list = sys.argv[1:]
    junit_output = [arg for arg in arg_list if "--junitxml" in arg]
    if junit_output:
        junit_logfile = junit_output.pop().split('--junitxml=')[1]
        xml_dumper = MultiRunXml(logfile=junit_logfile, prefix=None)
        xml_dumper.prefix = "FirstRun"
        pytest.main(arg_list, plugins=[xml_dumper])
        xml_dumper.prefix = "SecondRun"
        pytest.main(arg_list, plugins=[xml_dumper])
        xml_dumper.dump()

Notes: This runs pytest on the list of input tests twice. It is not a post-pytest merger of the test results.
Usage:

python -m MutliRunXml.py tests/test*.py --junitxml=./test-reports/junit.xml