fix(prefer-spy-on): improve autofix (#1308)

Author: FloEdelmann

src/rules/__tests__/prefer-spy-on.test.ts

@@ -106,5 +106,38 @@ ruleTester.run('prefer-spy-on', rule, {
         },
       ],
     },
+    {
+      // https://github.com/jest-community/eslint-plugin-jest/issues/1304
+      code: 'foo[bar] = jest.fn().mockReturnValue(undefined)',
+      output:
+        'jest.spyOn(foo, bar).mockImplementation().mockReturnValue(undefined)',
+      errors: [
+        {
+          messageId: 'useJestSpyOn',
+          type: AST_NODE_TYPES.AssignmentExpression,
+        },
+      ],
+    },
+    {
+      // https://github.com/jest-community/eslint-plugin-jest/issues/1307
+      code: `
+        foo.bar = jest.fn().mockImplementation(baz => baz)
+        foo.bar = jest.fn(a => b).mockImplementation(baz => baz)
+      `,
+      output: `
+        jest.spyOn(foo, 'bar').mockImplementation(baz => baz)
+        jest.spyOn(foo, 'bar').mockImplementation(baz => baz)
+      `,
+      errors: [
+        {
+          messageId: 'useJestSpyOn',
+          type: AST_NODE_TYPES.AssignmentExpression,
+        },
+        {
+          messageId: 'useJestSpyOn',
+          type: AST_NODE_TYPES.AssignmentExpression,
+        },
+      ],
+    },
   ],
 });

src/rules/prefer-spy-on.ts

@@ -1,4 +1,4 @@
-import { AST_NODE_TYPES, TSESTree } from '@typescript-eslint/utils';
+import { AST_NODE_TYPES, TSESLint, TSESTree } from '@typescript-eslint/utils';
 import { createRule, getNodeName } from './utils';
 
 const findNodeObject = (
@@ -39,6 +39,27 @@ const getJestFnCall = (node: TSESTree.Node): TSESTree.CallExpression | null => {
   return getJestFnCall(obj);
 };
 
+const getAutoFixMockImplementation = (
+  jestFnCall: TSESTree.CallExpression,
+  context: TSESLint.RuleContext<'useJestSpyOn', unknown[]>,
+): string => {
+  const hasMockImplementationAlready =
+    jestFnCall.parent?.type === AST_NODE_TYPES.MemberExpression &&
+    jestFnCall.parent.property.type === AST_NODE_TYPES.Identifier &&
+    jestFnCall.parent.property.name === 'mockImplementation';
+
+  if (hasMockImplementationAlready) {
+    return '';
+  }
+
+  const [arg] = jestFnCall.arguments;
+  const argSource = arg && context.getSourceCode().getText(arg);
+
+  return argSource
+    ? `.mockImplementation(${argSource})`
+    : '.mockImplementation()';
+};
+
 export default createRule({
   name: __filename,
   meta: {
@@ -71,12 +92,13 @@ export default createRule({
           messageId: 'useJestSpyOn',
           fix(fixer) {
             const leftPropQuote =
-              left.property.type === AST_NODE_TYPES.Identifier ? "'" : '';
-            const [arg] = jestFnCall.arguments;
-            const argSource = arg && context.getSourceCode().getText(arg);
-            const mockImplementation = argSource
-              ? `.mockImplementation(${argSource})`
-              : '.mockImplementation()';
+              left.property.type === AST_NODE_TYPES.Identifier && !left.computed
+                ? "'"
+                : '';
+            const mockImplementation = getAutoFixMockImplementation(
+              jestFnCall,
+              context,
+            );
 
             return [
               fixer.insertTextBefore(left, `jest.spyOn(`),