Merge pull request #277 from twisted/parallel-coverage

support `coverage -p`

tox.ini

@@ -3,7 +3,7 @@ envlist =
     {py36,py37}-twisted_lowest,
     {pypy3,py36,py37,py38,py39}-twisted_latest,
     {pypy3,py36,py37,py38,py39}-twisted_trunk,
-    towncrier, twine, check-manifest, flake8, docs
+    twine, check-manifest, flake8, docs, coverage-report
 isolated_build = true
 
 [testenv]
@@ -22,9 +22,8 @@ passenv = TERM  # ensure colors
 commands =
     pip list
     python -Wall \
-    {envbindir}/coverage run \
+    {envbindir}/coverage run -p \
     {envbindir}/trial {posargs:treq}
-    coverage report -m
 
 [testenv:flake8]
 skip_install = True
@@ -57,6 +56,12 @@ changedir = docs
 commands =
     sphinx-build -b html . html
 
+[testenv:coverage-report]
+depends = pypy3,py36,py37,py38,py39
+commands =
+    coverage combine
+    coverage report
+
 [flake8]
 # This is a minimal Black-compatible config.
 # See https://black.readthedocs.io/en/stable/compatible_configs.html#flake8