improve test script name clarity; expand test docs; cleanup docker run script

Author: ahupp

test/README

@@ -1,10 +1,6 @@
-To run the tests across a selection of Ubuntu LTS versions:
+There are a few ways to run the python-magic tests
 
-docker build -t "python_magic/xenial:latest" -f test/Dockerfile_xenial .
-docker build -t "python_magic/bionic:latest" -f test/Dockerfile_bionic .
-docker build -t "python_magic/focal:latest" -f test/Dockerfile_focal .
-
-docker run python_magic/xenial:latest
-docker run python_magic/bionic:latest
-docker run python_magic/focal:latest
+ 1. `pytest` will run the test suite against your default version of python
+ 2. `./test/run_all_versions.py` will run the tests against all installed versions of python.
+ 3. `./test/run_all_docker_test.sh` will run against a variety of different Linux distributions, using docker.
 

test/run_all_docker_test.sh

@@ -0,0 +1,13 @@
+#!/bin/sh
+
+set -e
+set -x
+
+ROOT=$(dirname $0)/..
+cd $ROOT
+
+for f in test/docker/*; do 
+    H=$(docker build -q -f ${f} .)
+    docker run --rm $H
+done
+