python debug with pytest-cov

docs/posts/2024/2024-02-22-debugging-in-python.md

@@ -7,6 +7,7 @@ categories:
 comments: true
 date:
   created: 2024-02-22
+  modified: 2024-04-27
 ---
 
 # Debugging in Python
@@ -29,4 +30,22 @@ Do not use: `export PYTHONBREAKPOINT='IPython.core.debugger.set_trace'`, it open
 
 ## Setting debugger in Pytest
 
-Already mentioned in another post dedicated to [Python unittest](../2021/2021-06-12-python-unittest-cheet-sheet.md#pytest-pdb-pdbclsipythonterminaldebuggerterminalpdb).
+**Conflict with pytest-cov**: If you use `pytest-cov`, you must use `pytest --no-cov` if you want to set breakpoints in your tests. Otherwise, pytest will just skip the breakpoints. This is because `pytest-cov` uses `sys.settrace()` to track code coverage, which is in conflict with breakpoints. There's no final solution for this issue, a workaround is to whether use coverage or whether use debug. In an IDE session (VSCode for e.g.), we can use `make test` to launch the test and generate coverage report with `pytest --cov`, and then use VScode's built-in debugger to set breakpoints and launch the tests in debug mode. To achieve this:
+
+1. `pip install pytest-cov` (must be installed because next VSCode settings depend on it).
+2. Add the following to your VSCode user settings:
+
+    ```json title="VSCode settings.json" hl_lines="9"
+      "python.testing.pytestArgs": [
+        "tests",
+        "--color=yes",
+        // https://github.com/microsoft/vscode-python/issues/693#issuecomment-1356832568
+        // must install pytest-cov as --no-cov is its param
+        // and if --no-cov is not specify, breakpoint doesn't work in pytest debug
+        // from VSCode UI to enable pytest debug from command line, need to add
+        // --no-cov to the Pytest args manually.
+        "--no-cov"
+      ],
+    ```
+
+**Use IPython as debugger prompt**: [Python unittest](../2021/2021-06-12-python-unittest-cheet-sheet.md#pytest-pdb-pdbclsipythonterminaldebuggerterminalpdb).