cli: never treat success as a failure in e2e test

packages/cli/e2e-test/cli-e2e-test.js

@@ -221,6 +221,7 @@ async function testAppServe(pluginName, appDir) {
   });
   Browser.localhost('localhost', 3000);
 
+  let successful = false;
   try {
     const browser = new Browser();
 
@@ -232,6 +233,7 @@ async function testAppServe(pluginName, appDir) {
     );
 
     print('Both App and Plugin loaded correctly');
+    successful = true;
   } catch (error) {
     throw new Error(`App serve test failed, ${error}`);
   } finally {
@@ -239,7 +241,13 @@ async function testAppServe(pluginName, appDir) {
     killTree(startApp.pid);
   }
 
-  await waitForExit(startApp);
+  try {
+    await waitForExit(startApp);
+  } catch (error) {
+    if (!successful) {
+      throw error;
+    }
+  }
 }
 
 process.on('unhandledRejection', handleError);

packages/cli/e2e-test/helpers.js

@@ -38,12 +38,6 @@ function spawnPiped(cmd, options) {
     ...options,
   });
   child.on('error', handleError);
-  child.on('exit', code => {
-    if (code) {
-      print(`Child '${cmd.join(' ')}' exited with code ${code}`);
-      process.exit(code);
-    }
-  });
 
   const logPrefix = cmd.map(s => s.replace(/.+\//, '')).join(' ');
   child.stdout.on(