tox: remove outdate coverage targets (#13520)

Author: sobolevn

CONTRIBUTING.md

@@ -54,10 +54,16 @@ python3 runtests.py
 You can also use `tox` to run tests (`tox` handles setting up the test environment for you):
 ```
 tox -e py
+
+# Or some specific python version:
+tox -e py39
+
+# Or some specific command:
+tox -e lint
 ```
 
 Some useful commands for running specific tests include:
-```
+```bash
 # Use mypy to check mypy's own code
 python3 runtests.py self
 # or equivalently:

test-data/unit/README.md

@@ -176,6 +176,10 @@ full builtins and library stubs instead of minimal ones. Run them using
 Note that running more processes than logical cores is likely to
 significantly decrease performance.
 
+To run tests with coverage:
+
+    python3 -m pytest --durations 100 --cov mypy --cov-config setup.cfg  --cov-report=term-missing:skip-covered --cov-report=html
+
 
 Debugging
 ---------

tox.ini

@@ -14,36 +14,9 @@ isolated_build = true
 
 [testenv]
 description = run the test driver with {basepython}
-setenv = cov: COVERAGE_FILE={toxworkdir}/.coverage.{envname}
 passenv = PYTEST_XDIST_WORKER_COUNT PROGRAMDATA PROGRAMFILES(X86)
 deps = -rtest-requirements.txt
 commands = python -m pytest --durations 100 {posargs}
-           cov: python -m pytest --durations 100 {posargs: --cov mypy --cov-config setup.cfg}
-
-
-[testenv:coverage]
-description = [run locally after tests]: combine coverage data and create report
-deps =
-    coverage >= 4.5.1, < 5
-    diff_cover >= 1.0.5, <2
-skip_install = True
-passenv =
-    {[testenv]passenv}
-    DIFF_AGAINST
-setenv = COVERAGE_FILE={toxworkdir}/.coverage
-commands =
-    coverage combine --rcfile setup.cfg
-    coverage report -m --rcfile setup.cfg
-    coverage xml -o {toxworkdir}/coverage.xml --rcfile setup.cfg
-    coverage html -d {toxworkdir}/htmlcov --rcfile setup.cfg
-    diff-cover --compare-branch {env:DIFF_AGAINST:origin/master} {toxworkdir}/coverage.xml
-depends =
-    py36,
-    py37,
-    py38,
-    py39,
-    py310,
-parallel_show_output = True
 
 [testenv:lint]
 description = check the code style