Use relative paths for coverage, and correct windows paths.

.github/workflows/ci.yml

@@ -169,6 +169,12 @@ jobs:
       uses: actions/download-artifact@v2
       with:
         name: coverage-data
+    - name: Normalize paths in coverage data
+      if: matrix.platform == 'windows-latest'
+      run: |
+        for coverage in `ls .coverage.*`; do
+          sqlite3 $coverage "update file set path = replace(path, '\\', '/')"
+        done
     - name: Combine coverage & fail if it's <100%.
       run: |
         pwd

pyproject.toml

@@ -5,10 +5,14 @@ build-backend = "setuptools.build_meta"
 [tool.coverage.run]
 parallel = true
 branch = true
+relative_files = true
 source = ["src/briefcase"]
 
 [tool.coverage.report]
 show_missing = true
+skip_covered = true
+skip_empty = true
+precision = 1
 exclude_lines = [
     "pragma: no cover",
     "@(abc\\.)?abstractmethod",