fix(prefer-spy-on): fix Cannot read property 'type' of undefined (#199)

Fixes #198

Author: hanneslund

rules/__tests__/prefer-spy-on.test.js

@@ -13,6 +13,7 @@ ruleTester.run('prefer-spy-on', rule, {
   valid: [
     'Date.now = () => 10',
     'window.fetch = jest.fn',
+    'Date.now = fn()',
     'obj.mock = jest.something()',
     'const mock = jest.fn()',
     'mock = jest.fn()',

rules/prefer-spy-on.js

@@ -4,7 +4,10 @@ const getDocsUrl = require('./util').getDocsUrl;
 const getNodeName = require('./util').getNodeName;
 
 const getJestFnCall = node => {
-  if (node.type !== 'CallExpression' && node.type !== 'MemberExpression') {
+  if (
+    (node.type !== 'CallExpression' && node.type !== 'MemberExpression') ||
+    (node.callee && node.callee.type !== 'MemberExpression')
+  ) {
     return null;
   }