Add GitHub Actions workflow for tests

.github/workflows/test.yml

@@ -0,0 +1,36 @@
+name: Test
+
+on:
+  push:
+    branches: [ "main" ]
+  pull_request:
+    branches: [ "main" ]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        python-version: ["3.9", "3.13"]
+
+    steps:
+    - uses: actions/checkout@v4
+
+    - name: Set up Python ${{ matrix.python-version }}
+      uses: actions/setup-python@v4
+      with:
+        python-version: ${{ matrix.python-version }}
+
+    - name: Install dependencies
+      run: |
+        python -m pip install --upgrade pip
+        pip install -e .[dev]
+
+    - name: Test with pytest
+      run: |
+        pytest tests/ -v --tb=short
+
+    - name: Test CLI command
+      run: |
+        draw_tree

README.md

@@ -14,7 +14,7 @@ pip install -e .
 
 ## Requirements
 
-- Python 3.7+ (tested on 3.13)
+- Python 3.9+ (tested on 3.13)
 - LaTeX with TikZ (for PDF/PNG generation)
 - (optional) ImageMagick or Ghostscript or Poppler (for PNG generation)