Add pytest and coverage configuration

Add `pytest-cov` which automatically measures coverage while tests are
executing and update tox and ci build configuration accordingly.

Add configuration for coverage:
  1. Enable analysing logical branches
  2. Save coverage details as HTML for local development use
  3. Configure the HTML output to include coverage context: on the
     right-hand side of each covered code line there is an expandable
     section which lists every test that ran that line.

.coveragerc

@@ -1,10 +0,0 @@
-[report]
-omit =
-    */pyshared/*
-    */python?.?/*
-    */test/*
-exclude_lines =
-    assert False
-    raise NotImplementedError
-    if __name__ == .__main__.:
-    def __repr__

.github/workflows/ci.yaml

@@ -49,10 +49,11 @@ jobs:
         run: |
           tox -e py-test
 
-      - name: Test latest Python version with tox and get coverage
-        if: matrix.python-version == '3.x'
+      - name: Upload code coverage
+        if: matrix.python-version == '3.7' && matrix.platform == 'ubuntu-latest'
         run: |
-          tox -vv -e py-cov
+          pip install codecov || true
+          codecov || true
 
       - name: Test latest Python version with tox and mypy
         if: matrix.python-version == '3.x'
@@ -63,12 +64,6 @@ jobs:
         run: |
           tox -vv -e py-mypy
 
-      - name: Upload code coverage
-        if: matrix.python-version == '3.x'
-        run: |
-          pip install codecov || true
-          codecov || true
-
   test-docs:
     runs-on: ubuntu-latest
 

setup.cfg

@@ -1,3 +1,43 @@
+[tool:pytest]
+# do not litter the working directory
+cache_dir = /tmp/pytest_cache
+# slightly more verbose output
+console_output_style = count
+addopts =
+    # show all skipped/failed/xfailed tests in the summary except passed
+    -ra
+    --strict-config
+    # record coverage in these two packages
+    --cov=beets
+    --cov=beetsplug
+    # save xml for coverage upload
+    --cov-report=xml:.reports/coverage.xml
+    # save html files for local dev use
+    --cov-report=html:.reports/html
+    # record coverage across logical branches
+    --cov-branch
+    # show which tests cover specific lines in the code (available in HTML)
+    --cov-context=test
+
+[coverage:run]
+data_file = .reports/coverage/data
+branch = true
+relative_files = true
+
+[coverage:report]
+precision = 2
+skip_empty = true
+show_missing = true
+exclude_lines =
+    pragma: no cover
+    if TYPE_CHECKING
+    if typing.TYPE_CHECKING
+    raise AssertionError
+    raise NotImplementedError
+
+[coverage:html]
+show_contexts = true
+
 [flake8]
 min-version = 3.6
 accept-encodings = utf-8

setup.py

@@ -103,11 +103,11 @@ setup(
     extras_require={
         "test": [
             "beautifulsoup4",
-            "coverage",
             "flask",
             "mock",
             "pylast",
             "pytest",
+            "pytest-cov",
             "python-mpd2",
             "python3-discogs-client>=2.3.15",
             "py7zr",

tox.ini

@@ -25,8 +25,7 @@ deps =
     mypy: {[_mypy]deps}
 passenv = INTEGRATION_TEST
 commands =
-    test: python -bb -m pytest -rs {posargs}
-    cov: coverage run -m pytest -rs {posargs}
+    test: python -m pytest {posargs}
     lint: python -m flake8 {posargs} {[_lint]files}
     mypy: mypy -p beets -p beetsplug
     mypy: mypy test