ci(tdd): check previous tests for fail (#13)

If the first commit in a pull request starts with "feat", "fix" or "bug", this action checks whether tests from the main branch failed with the latest version of the binary, as they should. Otherwise the pull request is not covered with tests

.github/workflows/rust.yml

@@ -33,3 +33,13 @@ jobs:
       run: cargo build --release --verbose
     - name: Run tests
       run: cargo test --verbose
+    - name: TDD check old tests
+      run: |
+        first_commit_hash=$(git rev-list --max-parents=0 HEAD)
+        first_commit_message=$(git log -1 --pretty=%B $first_commit_hash)
+        case $first_commit_message in
+          fix*|feat*|bug*)
+            git checkout $first_commit_hash~1 -- tests
+            !cargo test --verbose
+            ;;
+        esac