diff --git a/lib/helper/coverage.js b/lib/helper/coverage.js
index 05514cc..22ae36b 100644
--- a/lib/helper/coverage.js
+++ b/lib/helper/coverage.js
@@ -29,14 +29,14 @@ module.exports = wd => {
   wd.addPromiseChainMethod('coverage', function(opts = {}) {
     let {
       coverageIgnore = program.coverageIgnore,
-      keys,
+      keys = [],
     } = opts;
     const tempDir = path.join(cwd, 'coverage', '.temp');
     _.mkdir(tempDir);
     return this.execute('return { allKeys: Object.keys(window.__coverage__) }')
       .then(async res => {
         const { allKeys } = res;
-        if (!keys) {
+        if (!keys.length && allKeys) {
           keys = allKeys;
         }
         if (coverageIgnore) {