Add installer integration tests

.github/workflows/ci.yaml

-name: ci
+name: Build
 
 on:
   push:
@@ -16,7 +16,7 @@ on:
 
 jobs:
   prebuild:
-    name: Pre-Build checks
+    name: Pre-build checks
     runs-on: ubuntu-latest
     timeout-minutes: 5
     env:

.github/workflows/installer.yml

+name: Installer integration
+
+on:
+  push:
+    branches:
+      - main
+    paths:
+      - "installer.sh"
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  ubuntu:
+    name: Test installer on Ubuntu
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repo
+        uses: actions/checkout@v2
+
+      - name: Install code-server
+        run: ./install.sh
+
+      - name: Test code-server
+        run: yarn test:standalone-release code-server
+
+  macos:
+    name: Test installer on macOS
+    runs-on: macos-latest
+
+    steps:
+      - name: Checkout repo
+        uses: actions/checkout@v2
+
+      - name: Install code-server
+        run: ./install.sh
+
+      - name: Test code-server
+        run: yarn test:standalone-release code-server

ci/build/test-standalone-release.sh

 #!/usr/bin/env bash
 set -euo pipefail
 
-# Makes sure the release works.
+# Make sure a code-server release works. You can pass in the path otherwise it
+# will use release-standalone in the current directory.
+#
 # This is to make sure we don't have Node version errors or any other
 # compilation-related errors.
 main() {
@@ -10,12 +12,14 @@ main() {
   local EXTENSIONS_DIR
   EXTENSIONS_DIR="$(mktemp -d)"
 
-  echo "Testing standalone release."
+  local path=${1:-./release-standalone/bin/code-server}
 
-  # Note: using a basic theme extension because it doesn't update often and is more reliable for testing
-  ./release-standalone/bin/code-server --extensions-dir "$EXTENSIONS_DIR" --install-extension wesbos.theme-cobalt2
+  echo "Testing standalone release in $path."
+
+  # NOTE: using a basic theme extension because it doesn't update often and is more reliable for testing
+  "$path" --extensions-dir "$EXTENSIONS_DIR" --install-extension wesbos.theme-cobalt2
   local installed_extensions
-  installed_extensions="$(./release-standalone/bin/code-server --extensions-dir "$EXTENSIONS_DIR" --list-extensions 2>&1)"
+  installed_extensions="$("$path" --extensions-dir "$EXTENSIONS_DIR" --list-extensions 2>&1)"
   # We use grep as wesbos.theme-cobalt2 may have dependency extensions that change.
   if ! echo "$installed_extensions" | grep -q "wesbos.theme-cobalt2"; then
     echo "Unexpected output from listing extensions:"