Add basic GUI tests

Author: mfisher87

.github/workflows/test.yml

@@ -26,10 +26,19 @@ jobs:
         with:
           python-version: "${{ matrix.python-version }}"
 
-      - name: "Install dependencies in pyproject.toml"
+      - name: "Install test and project dependencies"
         run: |
+          # Project dependencies from pyproject.toml
+          # NOTE: Also builds viscm. How do we avoid this?
           pip install .
-          pip install pytest pytest-cov ${{ matrix.pyqt-dependency }}
+
+          # Test dependencies
+          pip install pytest pytest-cov pytest-qt pytest-xvfb ${{ matrix.pyqt-dependency }}
+          # pytest-qt CI dependencies: https://pytest-qt.readthedocs.io/en/latest/troubleshooting.html#github-actions
+          sudo apt update
+          sudo apt install -y \
+            xvfb \
+            libxkbcommon-x11-0 libxcb-icccm4 libxcb-image0 libxcb-keysyms1 libxcb-randr0 libxcb-render-util0 libxcb-xinerama0 libxcb-xfixes0 x11-utils
 
       - name: "Run tests"
         run: "make test"

Makefile

@@ -1,7 +1,7 @@
 .PHONY: test
 test:
 	python -m pytest --version
-	python -m pytest -v test/
+	python -m pytest --xvfb-backend=xvfb -v test/
 
 
 .PHONY: lint 

doc/contributing.md

@@ -2,28 +2,37 @@
 
 Install development dependencies:
 
-```
+```bash
 conda env create  # or `mamba env create`
 ```
 
 
 ## Development install
 
-```
+```bash
 pip install -e .
 ```
 
 
 ## Testing the build
 
-```
+```bash
 rm -rf dist
 python -m build
 pip install dist/*.whl  # or `dist/*.tar.gz`
 ```
 
 
-## Code formatting and linting
+## Tests
+
+See `Makefile` for convenience commands.
+
+
+### Code linting (and formatting)
+
+```bash
+make lint
+```
 
 This codebase uses [black](https://black.readthedocs.io/en/stable/) and
 [ruff](https://github.com/charliermarsh/ruff) to automatically format and lint the code.
@@ -37,3 +46,18 @@ and then another commit should immediately follow which updates
 `.git-blame-ignore-revs`. For example:
 [1fec42d](https://github.com/matplotlib/viscm/pull/64/commits/1fec42d0baf90e00d510efd76cb6006fa0c70dc4),
 [8aa7bb0](https://github.com/matplotlib/viscm/pull/64/commits/8aa7bb01440aeca6f8bbcefe0671c28f2ce284c6).
+
+
+### Unit tests
+
+```bash
+make test
+```
+
+Unit tests require `xvfb` (X Virtual Framebuffer) to test the GUI. If `xvfb` is not
+installed, you'll receive `ERROR: xvfb backend xvfb requested but not installed`.
+Install with:
+
+```bash
+sudo apt install xvfb
+```

test/conftest.py

@@ -0,0 +1,10 @@
+from pathlib import Path
+
+import pytest
+
+
+@pytest.fixture
+def tests_data_dir() -> Path:
+    tests_dir = Path(__file__).parent.resolve()
+    tests_data_dir = tests_dir / "data"
+    return tests_data_dir