Add Python script to run Rspec tests in docker container

This builds on the Ruby Test Explorer VSCode extension.
See my comment here: connorshea/vscode-ruby-test-adapter#30 (comment)

.rspec

@@ -1,3 +1 @@
---color
---require rails_helper
---format documentation
+--require rails_helper

spec/rspec_inside_docker.py

@@ -0,0 +1,71 @@
+# call this file: rspec_inside_docker.py
+# and put it in your ./spec/ folder
+
+# Specify the following (or alike) in your settings.json
+# "rubyTestExplorer.testFramework": "rspec",
+# "rubyTestExplorer.rspecCommand": "python3 ./spec/rspec_inside_docker.py",
+# "rubyTestExplorer.rspecDirectory": "./spec/",
+# "rubyTestExplorer.logpanel": true,
+# "rubyTestExplorer.filePattern": ["*_spec.rb"],
+
+import sys
+import subprocess
+
+# Path where the custom formatter of the Ruby Test explorer extension is memory-mapped
+FORMATTER_PATH_IN_DOCKER = "/root/tmp/formatter.rb"
+PROJECT_ROOT_FOLDER_NAME = "mampf"
+DOCKER_SERVICE_NAME = "mampf"
+
+
+def switch_formatter_path():
+    """
+    Memory-maps the custom formatter of the Ruby Test explorer extension.
+
+    The Ruby Test explorer extension uses a custom formatter to get a specific
+    output JSON format. The path to the formatter is automatically passed as an
+    argument to the rspec command by the extension. We need to replace this
+    path by the path to the memory-mapped formatter in the Docker container.
+    """
+
+    formatter_argument_index = None
+    for i, arg in enumerate(sys.argv):
+        if arg == '--require':
+            formatter_argument_index = i
+            break
+
+    if formatter_argument_index == None:
+        print('Please specify "--require path/to/custom/formatter.rb"')
+        sys.exit(1)
+
+    # Switch the path to the custom formatter to the memory-mapped path
+    formatter_path_on_host = sys.argv[formatter_argument_index + 1]
+    sys.argv[formatter_argument_index + 1] = FORMATTER_PATH_IN_DOCKER
+
+    return formatter_path_on_host
+
+
+def process_paths():
+    for i, arg in enumerate(sys.argv):
+        if not arg.startswith('./') and "spec" in arg:
+            sys.argv[i] = replace_absolute_paths_by_relative_paths(sys.argv[i])
+
+
+def replace_absolute_paths_by_relative_paths(path):
+    res = path.split(PROJECT_ROOT_FOLDER_NAME + '/')[1]
+    if not res:
+        print(f'Path {path}'
+              f' does not contain string "{PROJECT_ROOT_FOLDER_NAME}/"')
+        sys.exit(1)
+    return './' + res  # make path relative
+
+
+if __name__ == '__main__':
+    formatter_path_on_host = switch_formatter_path()
+    process_paths()
+
+    rspec_args = ' '.join(sys.argv[1:])
+    test_command = f'RAILS_ENV=test bundle exec rspec {rspec_args}'
+
+    docker_cmd = f'cd ./docker/run_cypress_tests && docker compose run --rm -T --entrypoint="" -v {formatter_path_on_host}:{FORMATTER_PATH_IN_DOCKER} {DOCKER_SERVICE_NAME} sh -c "{test_command}"'
+
+    subprocess.call(docker_cmd, shell=True)