added heartbeat functionality

src/launcher/launcher.ts

@@ -31,9 +31,33 @@ export function SaucelabsLauncher(args,
   // Array of connected drivers. This is useful for quitting all connected drivers on kill.
   let connectedDrivers: WebDriver[] = [];
 
+  // number of pending cancellations for heartbeat functionality
+  let pendingCancellations = 0;
+
   // Setup Browser name that will be printed out by Karma.
   this.name = browserName + ' on SauceLabs';
 
+  let pendingHeartBeat; 
+  const formatSauceError = (err) => {
+    return err.message + '\n' + (err.data ? '  ' + err.data : '')
+  }
+  // Heartbeat function to keep alive sessions on Sauce Labs via webdriver JSON wire calls
+  const heartbeat = () => {
+    pendingHeartBeat = setTimeout( (driver) => {
+      log.debug('Heartbeat to Sauce Labs (%s) - fetching title', browserName)
+
+      driver.title()
+        .then(null, (err) => {
+          log.error('Heartbeat to %s failed\n  %s', browserName, formatSauceError(err))
+
+          clearTimeout(pendingHeartBeat)
+          return this._done('failure')
+      });
+
+      heartbeat()
+      }, 60000);
+}
+
   // Listen for the start event from Karma. I know, the API is a bit different to how you
   // would expect, but we need to follow this approach unless we want to spend more work
   // improving type safety.
@@ -74,7 +98,13 @@ export function SaucelabsLauncher(args,
       browserMap.set(this.id, {sessionId, username, accessKey, proxy: sauceApiProxy});
 
       await driver.get(pageUrl);
+      heartbeat();
     } catch (e) {
+      // determine if there are still pending cancellations based on the heartbeat
+      if (pendingCancellations > 0) {
+        pendingCancellations--;
+        return;
+      }
       log.error(e);
 
       // Notify karma about the failure.
@@ -83,6 +113,11 @@ export function SaucelabsLauncher(args,
   });
 
   this.on('kill', async (doneFn: () => void) => {
+    // If there is still pending heartbeats, clear the timeout
+    if (pendingHeartBeat) {
+      clearTimeout(pendingHeartBeat);
+    }
+
     try {
       await Promise.all(connectedDrivers.map(driver => driver.quit()));
     } catch (e) {