Run pytest on GH (#22)

This PR adds an action to run pytest, so we can ensure we don't
accidentally break code.

.github/workflows/run-pytest.yaml

@@ -0,0 +1,32 @@
+name: Run Pytest
+
+on:
+  pull_request:
+  push:
+    branches: [main]
+
+jobs:
+  pytest:
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v4
+
+    - name: Setup python
+      uses: actions/setup-python@v5
+      with:
+        python-version: '3.10'
+
+    - name: Install global dependencies
+      run: |
+        pip install poetry
+        pip install pytest
+        pip install dendropy
+        pip install typing-extensions
+
+    - name: Test in ${{matrix.directories}}
+      working-directory: ${{matrix.directories}}
+      run: |
+        poetry install
+        poetry run pytest -v