Check for browsers in verifyOptions, so the script fails early.

test/test.py

@@ -37,6 +37,8 @@ class TestOptions(OptionParser):
             options.manifestFile = DEFAULT_MANIFEST_FILE
         if options.browser and options.browserManifestFile:
             print "Warning: ignoring browser argument since manifest file was also supplied"
+        if not options.browser and not options.browserManifestFile:
+            self.error("No test browsers found. Use --browserManifest or --browser args.")
         return options
         
 def prompt(question):
@@ -220,8 +222,7 @@ def setUp(options):
         testBrowsers = makeBrowserCommands(options.browserManifestFile)
     elif options.browser:
         testBrowsers = [BrowserCommand({"path":options.browser, "name":"firefox"})]
-    else:
+    assert len(testBrowsers) > 0
-        print "No test browsers found. Use --browserManifest or --browser args."
 
     with open(options.manifestFile) as mf:
         manifestList = json.load(mf)