Python coverage measurement and reporting in CI

<p>I want to measure test coverage in my Python project, enforce minimum coverage thresholds in CI, and track coverage changes over time. I use pytest and want coverage reported in the CI run.</p>

<p>pytest-cov with threshold enforcement:</p> <div class="highlight"><pre><span></span><code><span class="c1"># pyproject.toml</span> <span class="k">[tool.pytest.ini_options]</span> <span class="n">addopts</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s2">"--cov=app --cov-report=term-missing --cov-report=xml --cov-fail-under=80"</span> <span class="n">testpaths</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">[</span><span class="s2">"tests"</span><span class="p">]</span> <span class="k">[tool.coverage.run]</span> <span class="n">source</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">[</span><span class="s2">"app"</span><span class="p">]</span> <span class="n">omit</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">[</span> <span class="w"> </span><span class="s2">"app/migrations/*"</span><span class="p">,</span> <span class="w"> </span><span class="s2">"app/tests/*"</span><span class="p">,</span> <span class="w"> </span><span class="s2">"*/__init__.py"</span><span class="p">,</span> <span class="p">]</span> <span class="n">branch</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">true</span><span class="w"> </span><span class="c1"># Measure branch coverage too</span> <span class="k">[tool.coverage.report]</span> <span class="n">exclude_lines</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">[</span> <span class="w"> </span><span class="s2">"pragma: no cover"</span><span class="p">,</span> <span class="w"> </span><span class="s2">"if TYPE_CHECKING:"</span><span class="p">,</span> <span class="w"> </span><span class="s2">"raise NotImplementedError"</span><span class="p">,</span> <span class="w"> </span><span class="s2">"if __name__ == .__main__.:"</span><span class="p">,</span> <span class="p">]</span> </code></pre></div> <p>GitHub Actions with Codecov:</p> <div class="highlight"><pre><span></span><code><span class="nt">steps</span><span class="p">:</span> <span class="w"> </span><span class="p p-Indicator">-</span><span class="w"> </span><span class="nt">name</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">Run tests with coverage</span> <span class="w"> </span><span class="nt">run</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">uv run pytest</span> <span class="w"> </span><span class="p p-Indicator">-</span><span class="w"> </span><span class="nt">name</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">Upload to Codecov</span> <span class="w"> </span><span class="nt">uses</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">codecov/codecov-action@v4</span> <span class="w"> </span><span class="nt">with</span><span class="p">:</span> <span class="w"> </span><span class="nt">token</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">${{ secrets.CODECOV_TOKEN }}</span> <span class="w"> </span><span class="nt">files</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">coverage.xml</span> <span class="w"> </span><span class="nt">fail_ci_if_error</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">true</span> <span class="c1"># Add to PR comments:</span> <span class="w"> </span><span class="p p-Indicator">-</span><span class="w"> </span><span class="nt">name</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">Coverage summary</span> <span class="w"> </span><span class="nt">uses</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">irongut/CodeCoverageSummary@v1.3.0</span> <span class="w"> </span><span class="nt">with</span><span class="p">:</span> <span class="w"> </span><span class="nt">filename</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">coverage.xml</span> <span class="w"> </span><span class="nt">badge</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">true</span> <span class="w"> </span><span class="nt">fail_below_min</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">true</span> <span class="w"> </span><span class="nt">thresholds</span><span class="p">:</span><span class="w"> </span><span class="s">'80</span><span class="nv"> </span><span class="s">90'</span><span class="w"> </span><span class="c1"># Warning at 80, fail at &lt;80</span> </code></pre></div> <p>Mark untestable code:</p> <div class="highlight"><pre><span></span><code><span class="k">def</span><span class="w"> </span><span class="nf">unreachable_code</span><span class="p">():</span> <span class="c1"># pragma: no cover</span> <span class="w"> </span><span class="sd">"""Defensive code that cannot be triggered in practice."""</span> <span class="k">raise</span> <span class="ne">RuntimeError</span><span class="p">(</span><span class="s1">'Should never reach here'</span><span class="p">)</span> </code></pre></div> <p>Key points: - --cov-fail-under=80 fails the test run if coverage drops below 80% - branch=true catches untested code paths within functions - Codecov tracks coverage trends over time and comments on PRs - coverage.xml (machine-readable) + term-missing (human-readable) for CI - Exclude generated code and type stubs from coverage measurement</p>