Allow for extra Playwright CLI options when running e2e tests (#1768)

Resolves #1696

This PR allows for extra Playwright CLI options to passed to Playwright
when running e2e tests.

For example, this means you can guide Playwright on which tests to run
like so:
```bash
./dev-scripts/run-e2e-tests -- --grep 'shows privacy policy'
```

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href="https://codeapprove.com/pr/tiny-pilot/tinypilot/1768"><img
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dev-scripts/run-e2e-tests

@@ -10,27 +10,62 @@ set -e
 
 print_help() {
   cat << EOF
-Usage: ${0##*/} [target URL]
+Usage: ${0##*/} [--help] [--base-url E2E_BASE_URL] [-- [PLAYWRIGHT_ARGS]]
 Run end-to-end tests of UI navigation.
-  target URL: URL of running TinyPilot server to test against.
-    Must start with 'http'.
-    If not specified, the script first starts a local dev server.
-  -h Display this help and exit.
+  --help                  Optional. Display this help and exit.
+  --base-url E2E_BASE_URL Optional. The base URL of the running TinyPilot server
+                          to test against. Must start with 'http'. If not
+                          specified, the script will start a local dev server.
+  -- PLAYWRIGHT_ARGS      Optional. Indicate the end of this script's CLI
+                          options and add Playwright CLI test options.
+                          See https://playwright.dev/docs/test-cli#reference
+                          For example:
+                            run-e2e-tests -- --grep 'shows privacy policy'
+
 EOF
 }
 
 # Parse command-line arguments.
-while getopts 'h' opt; do
-  case "${opt}" in
-    h)
+E2E_BASE_URL=''
+PLAYWRIGHT_ARGS=()
+while [[ "$#" -gt 0 ]]; do
+  case "$1" in
+    --help)
       print_help
       exit
       ;;
+    --base-url)
+      if [[ "$#" -lt 2 ]]; then
+        shift;
+        break;
+      fi
+      E2E_BASE_URL="$2"
+      shift # For flag name.
+      shift # For flag value.
+      ;;
+    --)
+      # Stop parsing command-line arguments, and capture all remaining
+      # args to pass them through to Playwright.
+      shift
+      PLAYWRIGHT_ARGS=("$@")
+      break
+      ;;
     *)
-      print_help >&2
+      >&2 echo "Unknown flag: $1"
+      >&2 print_help
       exit 1
+      ;;
   esac
 done
+readonly E2E_BASE_URL
+readonly PLAYWRIGHT_ARGS
+
+if [[ -n "${E2E_BASE_URL}" && ! "${E2E_BASE_URL[0]}" =~ ^http ]]; then
+  >&2 echo "Invalid base URL: ${E2E_BASE_URL}"
+  >&2 echo 'The base URL must start with "http"'
+  >&2 print_help
+  exit 1
+fi
 
 # Echo commands before executing them, by default to stderr.
 set -x
@@ -40,13 +75,10 @@ SCRIPT_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" &> /dev/null && pwd )"
 readonly SCRIPT_DIR
 cd "${SCRIPT_DIR}/.."
 
-# If the first argument starts with http, strip it to export it as E2E_BASE_URL
-# That way, playwright.config.js can use it to override the default base URL and
-# will not start a local webserver.
-if [[ $# -gt 0 && "$1" =~ ^http ]]; then
-  export E2E_BASE_URL="$1"
-  readonly E2E_BASE_URL
-  shift
+if [[ -n "${E2E_BASE_URL}" ]]; then
+  # Indicate to playwright.config.js to override the default base URL and not to
+  # start a local webserver.
+  export E2E_BASE_URL
 else
   # When running against a local dev server, use a fresh home directory on each
   # test run so that database state in one run doesn't affect subsequent runs.
@@ -55,4 +87,7 @@ else
   readonly TINYPILOT_HOME_DIR
 fi
 
-npx playwright test
+# To avoid an "unbound variable" error, we only expand the PLAYWRIGHT_ARGS when
+# the array is not empty.
+# https://stackoverflow.com/a/7577209/3769045
+npx playwright test "${PLAYWRIGHT_ARGS[@]+"${PLAYWRIGHT_ARGS[@]}"}"