Add coverage commenting

.github/workflows/test.yaml

@@ -2,6 +2,7 @@ name: Python Tests
 
 permissions:
   contents: read
+  pull-requests: write
 
 on:
   push:
@@ -72,10 +73,30 @@ jobs:
           -m "full_pipeline" \
           --runner=docker \
           --junitxml=pytest-full.xml \
+          --cov-report=xml:coverage.xml \
           --cov=src tests \
           --cov-append \
           --verbose
 
+    - name: Generate combined coverage report
+      if: matrix.os == 'ubuntu-latest'
+      shell: bash
+      run: >
+        uv run coverage xml -o coverage.xml
+
+    - name: Merge JUnitXml files
+      if: matrix.os == 'ubuntu-latest'
+      shell: bash
+      run: >
+        uv run scripts/merge_cov_junitxml.py
+
+    - name: Pytest coverage comment
+      if: matrix.os == 'ubuntu-latest'
+      uses: MishaKav/pytest-coverage-comment@v1
+      with:
+        pytest-xml-coverage-path: ./coverage.xml
+        junitxml-path: ./pytest.xml
+
   ruff:
     runs-on: ubuntu-latest
     steps:

scripts/merge_cov_junitxml.py

@@ -0,0 +1,29 @@
+# /// script
+# dependencies = ["junitparser"]
+# requires-python = ">=3.12"
+# ///
+"""Merge pytest-cov's junitxml file for codecov commenting.
+
+Reads all generated junitxml files and generates:
+  - pytest.xml (merged xml file)
+
+Run with:
+    uv run scripts/merge_cov_junitxml.py
+"""
+
+from pathlib import Path
+
+from junitparser import JUnitXml
+
+
+def main() -> None:
+    """Merge generated junitxml files."""
+    merged = JUnitXml()
+    for f in ["pytest-quick.xml", "pytest-slow.xml", "pytest-full.xml"]:
+        if Path(f).exists():
+            merged += JUnitXml.fromfile(f)
+    merged.write("pytest.xml")
+
+
+if __name__ == "__main__":
+    main()