Add some basic testing environment info.

README.rst

@@ -38,7 +38,7 @@ If you notice any differences, please report them.
 Requirements
 ------------
 
-- python 3.7+
+- python 3.8+
 - pygobject
 - glib
 - gtk+3 (optional)
@@ -129,6 +129,39 @@ actually prevent you from doing that (in accordance with PEP 3156), however
 in mind that enclosed loops may be started at any time by third-party code
 calling GLib's primitives.
 
+Testing
+-------
+
+Testing GBulb requires a Linux environment that has GLib and GTK development
+libraries available.
+
+The tests folder contains a Dockerfile that defines a complete testing
+environment. To use the Docker environment, run the following from the root of
+the git checkout:
+
+   $ docker buildx build --tag beeware/gbulb:latest --file ./tests/Dockerfile .
+   $ docker run --rm --volume $(PWD):/home/brutus/gbulb:z -it beeware/gbulb:latest
+
+This will drop you into an Ubuntu 24.04 shell that has Python 3.8-3.13
+installed, mounting the current working directory as `/home/brutus/gbulb`. You
+can use this to create virtual environments for each Python version.
+
+Once you have an active virtual environment, run:
+
+   (venv) $ pip install -e .[dev]
+   (venv) $ pytest
+
+to run the test suite. Alternatively, you can install tox, and then run:
+
+   # To test a single Python version
+   (venv) $ tox -e py
+
+   # To test Python 3.10 specifically
+   (venv) $ tox -e py310
+
+   # To test all versions
+   (venv) $ tox
+
 Community
 ---------
 

tests/Dockerfile

@@ -0,0 +1,48 @@
+FROM ubuntu:24.04
+
+# Disable pip's warnings and SDL audio
+ENV PIP_ROOT_USER_ACTION=ignore \
+    PIP_NO_WARN_SCRIPT_LOCATION=0 \
+    SDL_AUDIODRIVER=dummy
+
+# Run apt non-interactively; use ARG so this only applies while building the image
+ARG DEBIAN_FRONTEND="noninteractive"
+
+# Add deadsnakes
+RUN apt-get update -y && \
+    apt-get install --no-install-recommends -y software-properties-common && \
+    add-apt-repository ppa:deadsnakes/ppa
+
+# Install System python
+RUN apt-get update -y && \
+    apt-get install --no-install-recommends -y \
+        libgirepository1.0-dev \
+        gir1.2-gtk-3.0 \
+        libcairo2-dev \
+        build-essential \
+        git \
+        python3.8-dev \
+        python3.8-venv \
+        python3.9-dev \
+        python3.9-venv \
+        python3.10-dev \
+        python3.10-venv \
+        python3.11-dev \
+        python3.11-venv \
+        python3-dev \
+        python3-venv \
+        python3.13-dev \
+        python3.13-venv \
+        python3-pip
+
+RUN groupadd beeware && \
+    useradd brutus -g beeware --home /home/brutus && \
+    mkdir -p /home/brutus && chown brutus:beeware /home/brutus
+
+# Use the brutus user for operations in the container
+USER brutus
+
+# Set the working directory
+WORKDIR /home/brutus/gbulb
+
+CMD /bin/bash