From d9a79b23ed990bada8a9fbbf4e331583f78ab0ca Mon Sep 17 00:00:00 2001
From: Chris Blossom <cbloss@gmail.com>
Date: Mon, 12 Aug 2019 16:27:31 -0700
Subject: [PATCH] fix(prefer-spy-on): do not change behavior of fixed instances
 (#390)

Fixes #389
---
 src/rules/__tests__/prefer-spy-on.test.ts | 11 ++++++-----
 src/rules/prefer-spy-on.ts                |  2 +-
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/src/rules/__tests__/prefer-spy-on.test.ts b/src/rules/__tests__/prefer-spy-on.test.ts
index 2bf82f79e..b95d13e2d 100644
--- a/src/rules/__tests__/prefer-spy-on.test.ts
+++ b/src/rules/__tests__/prefer-spy-on.test.ts
@@ -31,7 +31,7 @@ ruleTester.run('prefer-spy-on', rule, {
           type: AST_NODE_TYPES.AssignmentExpression,
         },
       ],
-      output: "jest.spyOn(obj, 'a'); const test = 10;",
+      output: "jest.spyOn(obj, 'a').mockImplementation(); const test = 10;",
     },
     {
       code: "Date['now'] = jest['fn']()",
@@ -41,7 +41,7 @@ ruleTester.run('prefer-spy-on', rule, {
           type: AST_NODE_TYPES.AssignmentExpression,
         },
       ],
-      output: "jest.spyOn(Date, 'now')",
+      output: "jest.spyOn(Date, 'now').mockImplementation()",
     },
     {
       code: 'window[`${name}`] = jest[`fn`]()',
@@ -51,7 +51,7 @@ ruleTester.run('prefer-spy-on', rule, {
           type: AST_NODE_TYPES.AssignmentExpression,
         },
       ],
-      output: 'jest.spyOn(window, `${name}`)',
+      output: 'jest.spyOn(window, `${name}`).mockImplementation()',
     },
     {
       code: "obj['prop' + 1] = jest['fn']()",
@@ -61,7 +61,7 @@ ruleTester.run('prefer-spy-on', rule, {
           type: AST_NODE_TYPES.AssignmentExpression,
         },
       ],
-      output: "jest.spyOn(obj, 'prop' + 1)",
+      output: "jest.spyOn(obj, 'prop' + 1).mockImplementation()",
     },
     {
       code: 'obj.one.two = jest.fn(); const test = 10;',
@@ -71,7 +71,8 @@ ruleTester.run('prefer-spy-on', rule, {
           type: AST_NODE_TYPES.AssignmentExpression,
         },
       ],
-      output: "jest.spyOn(obj.one, 'two'); const test = 10;",
+      output:
+        "jest.spyOn(obj.one, 'two').mockImplementation(); const test = 10;",
     },
     {
       code: 'obj.a = jest.fn(() => 10)',
diff --git a/src/rules/prefer-spy-on.ts b/src/rules/prefer-spy-on.ts
index 5a6fff6a4..247704fce 100644
--- a/src/rules/prefer-spy-on.ts
+++ b/src/rules/prefer-spy-on.ts
@@ -79,7 +79,7 @@ export default createRule({
             const argSource = arg && context.getSourceCode().getText(arg);
             const mockImplementation = argSource
               ? `.mockImplementation(${argSource})`
-              : '';
+              : '.mockImplementation()';
 
             return [
               fixer.insertTextBefore(left, `jest.spyOn(`),