Wait for port to be freed before continuing

test/templates/util/ports.ts

@@ -0,0 +1,23 @@
+import * as portastic from 'portastic';
+const pollInterval = 500;
+
+export function waitUntilPortState(port: number, isOpen: boolean, timeoutMs: number, callback: (err: any) => void) {
+    if (!(timeoutMs > 0)) {
+        throw new Error(`Timed out after ${ timeoutMs }ms waiting for port ${ port } to become ${ isOpen ? 'free' : 'in use' }`);
+    }
+
+    portastic.test(port).then(
+        actualIsOpenState => {
+            if (actualIsOpenState === isOpen) {
+                // Desired state is reached
+                callback(null);
+            } else {
+                // Wait longer
+                setTimeout(() => {
+                    waitUntilPortState(port, isOpen, timeoutMs - pollInterval, callback);
+                }, pollInterval);
+            }
+        },
+        callback
+    )
+}