add more tests

Author: aminya

spec/spec.js

@@ -14,5 +14,37 @@ pluginTester({
       code: '"not strict";',
       output:'"not strict";',
     },
+    {
+      code: '"use strict";',
+      output: '"use strict";',
+    },
+    {
+      code: '"use strict"; "not strict";',
+      output:'"not strict";',
+    },
+    {
+      code: `
+      "use strict";
+      "not strict";
+
+      process.platform = "windows";
+      `,
+      output: `
+      "not strict";
+
+      process.platform = "windows";`,
+    },
+    {
+      code: `
+      "use strict";
+      "not strict";
+
+      let x = 1;
+      `,
+      output: `
+      "not strict";
+
+      let x = 1;`,
+    },
   ]
 })