[WIP] Add tests and coverage

Singularity.def

@@ -6,7 +6,7 @@ From: python:3.11-slim
     apt-get install -y --no-install-recommends imagemagick
     rm -rf /var/lib/apt/lists/*
 
-    pip install --no-cache-dir jinja2 pyyaml
+    pip install --no-cache-dir jinja2 pyyaml coverage pytest pytest-cov
     mkdir -p /src
 
 %files
@@ -17,4 +17,10 @@ From: python:3.11-slim
 
 %runscript
     cd /src
-    exec python3 generate_gallery.py "$@"
+    exec python3 generate_gallery.py "$@"
+
+%test
+    # Run container tests with coverage to validate the build
+    echo "Running container validation tests with coverage..."
+    cd /src
+    python3 tests/run_coverage.py