add test infrastructure for --nobs

Dockerfile

@@ -2,8 +2,11 @@ FROM python:2.7-slim
 
 WORKDIR /app
 
+# install dependencies (optional - bs4 can be skipped with --nobs)
+COPY requirements.txt .
+RUN pip install -r requirements.txt || true
+
 COPY . .
 
-RUN pip install -r requirements.txt
-
-CMD ["python", "ppf.py"]
+# default: run syntax check
+CMD ["python", "-m", "py_compile", "ppf.py", "soup_parser.py", "config.py", "fetch.py"]