diff --git a/lib/inject_context.js b/lib/inject_context.js
index bf06716..9186d66 100644
--- a/lib/inject_context.js
+++ b/lib/inject_context.js
@@ -1,4 +1,6 @@
+const assert = require('assert');
 const debug = require('util').debuglog('egg-mock:inject_context');
+const MOCHA_SUITE_APP = Symbol.for('mocha#suite#app');
 const appHandler = require('./app_handler');
 
 /**
@@ -42,7 +44,7 @@ function injectContext(mocha) {
     let errSuite;
     try {
       await app.ready();
-      suite.ctx.app = app;
+      suite.ctx[MOCHA_SUITE_APP] = app;
       const mockContextFun = app.mockModuleContextScope || app.mockContextScope;
       await mockContextFun.call(app, async function() {
         await new Promise(resolve => {
@@ -67,7 +69,7 @@ function injectContext(mocha) {
       return runTests.call(this, suite, fn);
     }
 
-    const app = suite.ctx.app;
+    const app = suite.ctx[MOCHA_SUITE_APP];
 
     const self = this;
     if (!app) {
@@ -89,6 +91,7 @@ function injectContext(mocha) {
       let app;
       try {
         app = await appHandler.getApp(suite, test);
+        assert(app, `not found app for test ${getTestTitle(suite, test)}`);
         await app.ready();
       } catch (err) {
         err.message = `[egg-mock/runTests] get app for ${getTestTitle(suite, test)}: ${err.message}`;