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feat(rules): no-standalone-expect (#350)
Fixes #342
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‎README.md

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@@ -123,6 +123,7 @@ installations requiring long-term consistency.
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| [no-jest-import][] | Disallow importing `jest` | ![recommended][] | |
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| [no-large-snapshots][] | Disallow large snapshots | | |
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| [no-mocks-import][] | Disallow manually importing from `__mocks__` | | |
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| [no-standalone-expect][] | Prevents `expect` statements outside of a `test` or `it` block | | |
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| [no-test-callback][] | Using a callback in asynchronous tests | | ![fixable-green][] |
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| [no-test-prefixes][] | Disallow using `f` & `x` prefixes to define focused/skipped tests | ![recommended][] | ![fixable-green][] |
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| [no-test-return-statement][] | Disallow explicitly returning from tests | | |
@@ -174,6 +175,7 @@ https://github.com/dangreenisrael/eslint-plugin-jest-formatting
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[no-jest-import]: docs/rules/no-jest-import.md
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[no-large-snapshots]: docs/rules/no-large-snapshots.md
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[no-mocks-import]: docs/rules/no-mocks-import.md
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[no-standalone-expect]: docs/rules/no-standalone-expect.md
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[no-test-callback]: docs/rules/no-test-callback.md
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[no-test-prefixes]: docs/rules/no-test-prefixes.md
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[no-test-return-statement]: docs/rules/no-test-return-statement.md

‎docs/rules/no-standalone-expect.md

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# No standalone expect in a describe block (no-standalone-expect)
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Prevents `expect` statements outside of a `test` or `it` block. An `expect`
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within a helper function (but outside of a `test` or `it` block) will not
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trigger this rule.
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## Rule Details
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This rule aims to eliminate `expect` statements that will not be executed. An
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`expect` inside of a `describe` block but outside of a `test` or `it` block or
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outside of a `describe` will not execute and therefore will trigger this rule.
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It is viable, however, to have an `expect` in a helper function that is called
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from within a `test` or `it` block so `expect` statements in a function will not
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trigger this rule.
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Statements like `expect.hasAssertions()` will NOT trigger this rule since these
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calls will execute if they are not in a test block.
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Examples of **incorrect** code for this rule:
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```js
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// in describe
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describe('a test', () => {
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expect(1).toBe(1);
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});
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// below other tests
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describe('a test', () => {
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it('an it', () => {
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expect(1).toBe(1);
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});
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expect(1).toBe(1);
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});
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```
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Examples of **correct** code for this rule:
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```js
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// in it block
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describe('a test', () => {
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it('an it', () => {
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expect(1).toBe(1);
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});
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});
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// in helper function
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describe('a test', () => {
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const helper = () => {
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expect(1).toBe(1);
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};
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it('an it', () => {
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helper();
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});
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});
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describe('a test', () => {
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expect.hasAssertions(1);
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});
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```
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\*Note that this rule will not trigger if the helper function is never used even
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thought the `expect` will not execute. Rely on a rule like no-unused-vars for
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this case.
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## When Not To Use It
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Don't use this rule on non-jest test files.

‎src/__tests__/rules.test.js

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@@ -3,7 +3,7 @@ import { resolve } from 'path';
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import { rules } from '../';
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const ruleNames = Object.keys(rules);
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const numberOfRules = 36;
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const numberOfRules = 37;
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describe('rules', () => {
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it('should have a corresponding doc for each rule', () => {

‎src/rules/__tests__/no-standalone-expect-test.ts

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import { TSESLint } from '@typescript-eslint/experimental-utils';
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import rule from '../no-standalone-expect';
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const ruleTester = new TSESLint.RuleTester({
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parserOptions: {
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ecmaVersion: 2015,
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},
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});
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ruleTester.run('no-standalone-expect', rule, {
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valid: [
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'describe("a test", () => { it("an it", () => {expect(1).toBe(1); }); });',
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'describe("a test", () => { it("an it", () => { const func = () => { expect(1).toBe(1); }; }); });',
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'describe("a test", () => { const func = () => { expect(1).toBe(1); }; });',
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'describe("a test", () => { function func() { expect(1).toBe(1); }; });',
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'describe("a test", () => { const func = function(){ expect(1).toBe(1); }; });',
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'it("an it", () => expect(1).toBe(1))',
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'const func = function(){ expect(1).toBe(1); };',
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'const func = () => expect(1).toBe(1);',
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'expect.hasAssertions()',
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'{}',
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'it.each([1, true])("trues", value => { expect(value).toBe(true); });',
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'it.each([1, true])("trues", value => { expect(value).toBe(true); }); it("an it", () => { expect(1).toBe(1) });',
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`
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it.each\`
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num | value
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\${1} | \${true}
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\`('trues', ({ value }) => {
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expect(value).toBe(true);
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});
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`,
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'it.only("an only", value => { expect(value).toBe(true); });',
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'describe.each([1, true])("trues", value => { it("an it", () => expect(value).toBe(true) ); });',
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],
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invalid: [
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{
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code: 'describe("a test", () => { expect(1).toBe(1); });',
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errors: [{ endColumn: 37, column: 28, messageId: 'unexpectedExpect' }],
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},
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{
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code: 'describe("a test", () => expect(1).toBe(1));',
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errors: [{ endColumn: 35, column: 26, messageId: 'unexpectedExpect' }],
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},
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{
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code:
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'describe("a test", () => { const func = () => { expect(1).toBe(1); }; expect(1).toBe(1); });',
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errors: [{ endColumn: 80, column: 71, messageId: 'unexpectedExpect' }],
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},
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{
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code:
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'describe("a test", () => { it(() => { expect(1).toBe(1); }); expect(1).toBe(1); });',
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errors: [{ endColumn: 72, column: 63, messageId: 'unexpectedExpect' }],
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},
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{
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code: 'expect(1).toBe(1);',
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errors: [{ endColumn: 10, column: 1, messageId: 'unexpectedExpect' }],
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},
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{
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code: 'expect(1).toBe',
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errors: [{ endColumn: 10, column: 1, messageId: 'unexpectedExpect' }],
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},
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{
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code: '{expect(1).toBe(1)}',
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errors: [{ endColumn: 11, column: 2, messageId: 'unexpectedExpect' }],
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},
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{
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code:
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'it.each([1, true])("trues", value => { expect(value).toBe(true); }); expect(1).toBe(1);',
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errors: [{ endColumn: 79, column: 70, messageId: 'unexpectedExpect' }],
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},
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{
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code:
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'describe.each([1, true])("trues", value => { expect(value).toBe(true); });',
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errors: [{ endColumn: 59, column: 46, messageId: 'unexpectedExpect' }],
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},
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],
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});

‎src/rules/no-standalone-expect.ts

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import {
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AST_NODE_TYPES,
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TSESTree,
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} from '@typescript-eslint/experimental-utils';
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import {
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TestCaseName,
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createRule,
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isDescribe,
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isExpectCall,
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isFunction,
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isTestCase,
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} from './tsUtils';
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const getBlockType = (
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stmt: TSESTree.BlockStatement,
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): 'function' | 'describe' | null => {
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const func = stmt.parent;
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/* istanbul ignore if */
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if (!func) {
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throw new Error(
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`Unexpected BlockStatement. No parent defined. - please file a github issue at https://github.com/jest-community/eslint-plugin-jest`,
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);
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}
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// functionDeclaration: function func() {}
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if (func.type === AST_NODE_TYPES.FunctionDeclaration) {
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return 'function';
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}
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if (isFunction(func) && func.parent) {
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const expr = func.parent;
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// arrowfunction or function expr
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if (expr.type === AST_NODE_TYPES.VariableDeclarator) {
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return 'function';
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}
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// if it's not a variable, it will be callExpr, we only care about describe
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if (expr.type === AST_NODE_TYPES.CallExpression && isDescribe(expr)) {
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return 'describe';
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}
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}
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return null;
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};
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const isEach = (node: TSESTree.CallExpression): boolean => {
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if (
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node &&
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node.callee &&
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node.callee.type === AST_NODE_TYPES.CallExpression &&
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node.callee.callee &&
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node.callee.callee.type === AST_NODE_TYPES.MemberExpression &&
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node.callee.callee.property &&
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node.callee.callee.property.type === AST_NODE_TYPES.Identifier &&
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node.callee.callee.property.name === 'each' &&
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node.callee.callee.object &&
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node.callee.callee.object.type === AST_NODE_TYPES.Identifier &&
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TestCaseName.hasOwnProperty(node.callee.callee.object.name)
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) {
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return true;
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}
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return false;
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};
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type callStackEntry =
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| 'test'
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| 'function'
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| 'describe'
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| 'arrowFunc'
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| 'template';
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export default createRule({
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name: __filename,
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meta: {
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docs: {
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category: 'Best Practices',
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description: 'Prevents expects that are outside of an it or test block.',
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recommended: false,
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},
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messages: {
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unexpectedExpect: 'Expect must be inside of a test block.',
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},
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type: 'suggestion',
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schema: [],
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},
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defaultOptions: [],
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create(context) {
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const callStack: callStackEntry[] = [];
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return {
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CallExpression(node) {
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if (isExpectCall(node)) {
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const parent = callStack[callStack.length - 1];
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if (!parent || parent === 'describe') {
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context.report({ node, messageId: 'unexpectedExpect' });
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}
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return;
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}
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if (isTestCase(node)) {
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callStack.push('test');
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}
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if (node.callee.type === AST_NODE_TYPES.TaggedTemplateExpression) {
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callStack.push('template');
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}
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},
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'CallExpression:exit'(node: TSESTree.CallExpression) {
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const top = callStack[callStack.length - 1];
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if (
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(((isTestCase(node) &&
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node.callee.type !== AST_NODE_TYPES.MemberExpression) ||
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isEach(node)) &&
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top === 'test') ||
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(node.callee.type === AST_NODE_TYPES.TaggedTemplateExpression &&
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top === 'template')
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) {
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callStack.pop();
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}
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},
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BlockStatement(stmt) {
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const blockType = getBlockType(stmt);
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if (blockType) {
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callStack.push(blockType);
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}
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},
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'BlockStatement:exit'(stmt: TSESTree.BlockStatement) {
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const blockType = getBlockType(stmt);
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if (blockType && blockType === callStack[callStack.length - 1]) {
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callStack.pop();
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}
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},
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ArrowFunctionExpression(node) {
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if (node.parent && node.parent.type !== AST_NODE_TYPES.CallExpression) {
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callStack.push('arrowFunc');
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}
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},
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'ArrowFunctionExpression:exit'() {
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if (callStack[callStack.length - 1] === 'arrowFunc') {
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callStack.pop();
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}
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},
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};
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},
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});

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