Always run the flutter tool in checked mode. (#11069)

(Needs https://github.com/dart-lang/sdk/issues/28519)

bin/flutter

@@ -65,8 +65,10 @@ if [ ! -d "$FLUTTER_ROOT/.git" ]; then
   exit 1
 fi
 
+FLUTTER_TOOL_ARGS="--checked"
+
 # To debug the tool, you can uncomment the following line to enable checked mode and set an observatory port:
-# FLUTTER_TOOL_ARGS="--observe=65432 --checked"
+# FLUTTER_TOOL_ARGS="$FLUTTER_TOOL_ARGS --observe=65432"
 
 (
   if hash flock 2>/dev/null; then

bin/flutter.bat

@@ -39,8 +39,10 @@ IF NOT EXIST "%flutter_root%\.git" (
 REM Ensure that bin/cache exists.
 IF NOT EXIST "%cache_dir%" MKDIR "%cache_dir%"
 
+SET FLUTTER_TOOL_ARGS="--checked"
+
 REM To debug the tool, you can uncomment the following line to enable checked mode and set an observatory port:
-REM SET FLUTTER_TOOL_ARGS="--observe=65432 --checked"
+REM SET FLUTTER_TOOL_ARGS="%FLUTTER_TOOL_ARGS% --observe=65432"
 
 :acquire_lock
 2>NUL (

packages/flutter_tools/lib/src/commands/test.dart

@@ -172,7 +172,7 @@ class TestCommand extends FlutterCommand {
       workDir = fs.directory('test');
       if (!workDir.existsSync())
         throwToolExit('Test directory "${workDir.path}" not found.');
-      files = _findTests(workDir);
+      files = _findTests(workDir).toList();
       if (files.isEmpty) {
         throwToolExit(
             'Test directory "${workDir.path}" does not appear to contain any test files.\n'