diff --git a/webdev/test/e2e_test.dart b/webdev/test/e2e_test.dart
index 2b6760256..066c62cda 100644
--- a/webdev/test/e2e_test.dart
+++ b/webdev/test/e2e_test.dart
@@ -39,6 +39,26 @@ void main() {
     await d.file('pubspec.lock', isNotEmpty).validate(exampleDirectory);
   });
 
+  test('build should fail if targetting an existing directory', () async {
+    await d.file('simple thing', 'throw-away').create();
+
+    var args = ['build', '-o', 'web:${d.sandbox}'];
+
+    var process = await runWebDev(args, workingDirectory: exampleDirectory);
+
+    // NOTE: We'd like this to be more useful
+    // See https://github.com/dart-lang/build/issues/1283
+
+    await expectLater(
+        process.stdout,
+        emitsThrough(
+            '[WARNING] Skipped creation of the merged output directory.'));
+    await expectLater(process.stderr,
+        emitsThrough('Failed to create merged output directories.'));
+
+    await process.shouldExit(1);
+  });
+
   group('should build with valid configuration', () {
     for (var withDDC in [true, false]) {
       test(withDDC ? 'DDC' : 'dart2js', () async {
@@ -50,10 +70,6 @@ void main() {
         var process = await runWebDev(args, workingDirectory: exampleDirectory);
 
         var expectedItems = <Object>['[INFO] Succeeded'];
-        if (!withDDC) {
-          expectedItems.add(anyOf(
-              contains('with 0 outputs'), contains('Running dart2js with')));
-        }
 
         await checkProcessStdout(process, expectedItems);
         await process.shouldExit(0);
diff --git a/webdev/test/integration_test.dart b/webdev/test/integration_test.dart
index 8e2411822..2ec64c6e0 100644
--- a/webdev/test/integration_test.dart
+++ b/webdev/test/integration_test.dart
@@ -42,8 +42,8 @@ name: sample
           var process = await runWebDev([command], workingDirectory: d.sandbox);
 
           await checkProcessStdout(process, [
-            r'''webdev could not run for this project.
-You must have a dependency on `build_runner` in `pubspec.yaml`.'''
+            'webdev could not run for this project.',
+            'You must have a dependency on `build_runner` in `pubspec.yaml`.'
           ]);
           await process.shouldExit(78);
         });
@@ -63,8 +63,8 @@ name: sample
           var process = await runWebDev(['serve'], workingDirectory: d.sandbox);
 
           await checkProcessStdout(process, [
-            r'''webdev could not run for this project.
-You must have a dependency on `build_web_compilers` in `pubspec.yaml`.'''
+            'webdev could not run for this project.',
+            'You must have a dependency on `build_web_compilers` in `pubspec.yaml`.'
           ]);
           await process.shouldExit(78);
         });
diff --git a/webdev/test/test_utils.dart b/webdev/test/test_utils.dart
index be1628f4f..46b286f56 100644
--- a/webdev/test/test_utils.dart
+++ b/webdev/test/test_utils.dart
@@ -19,11 +19,11 @@ Future<TestProcess> runWebDev(List<String> args, {String workingDirectory}) {
 }
 
 Future checkProcessStdout(TestProcess process, List items) async {
-  var output = await process.stdoutStream().join('\n');
   for (var item in items) {
     if (item is! Matcher) {
       item = contains(item);
     }
-    expect(output, item);
+
+    await expectLater(process.stdout, emitsThrough(item));
   }
 }