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Add no-negated-assertion rule
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‎docs/rules/no-negated-assertion.md‎

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# ava/no-negated-assertion
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📝 Disallow negated assertions.
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💼 This rule is enabled in the ✅ `recommended` [config](https://github.com/avajs/eslint-plugin-ava#recommended-config).
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🔧 This rule is automatically fixable by the [`--fix` CLI option](https://eslint.org/docs/latest/user-guide/command-line-interface#--fix).
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<!-- end auto-generated rule header -->
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Using negated arguments in assertions like `t.true(!x)` is harder to read than using the opposite assertion `t.false(x)`. This rule enforces using the positive assertion method instead of negating the argument.
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## Examples
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```js
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import test from 'ava';
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test('foo', t => {
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t.true(!value); // ❌
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t.false(value); // ✅
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t.false(!value); // ❌
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t.true(value); // ✅
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t.truthy(!value); // ❌
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t.falsy(value); // ✅
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t.falsy(!value); // ❌
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t.truthy(value); // ✅
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t.true(!!value); // ❌ (double negation is unnecessary)
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t.true(value); // ✅
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});
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```

‎index.js‎

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@@ -16,6 +16,7 @@ import noImportTestFiles from './rules/no-import-test-files.js';
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import noIncorrectDeepEqual from './rules/no-incorrect-deep-equal.js';
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import noInlineAssertions from './rules/no-inline-assertions.js';
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import noInvalidModifierChain from './rules/no-invalid-modifier-chain.js';
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import noNegatedAssertion from './rules/no-negated-assertion.js';
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import noNestedAssertions from './rules/no-nested-assertions.js';
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import noNestedTests from './rules/no-nested-tests.js';
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import noOnlyTest from './rules/no-only-test.js';
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'no-incorrect-deep-equal': noIncorrectDeepEqual,
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'no-inline-assertions': noInlineAssertions,
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'no-invalid-modifier-chain': noInvalidModifierChain,
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'no-negated-assertion': noNegatedAssertion,
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'no-nested-assertions': noNestedAssertions,
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'no-nested-tests': noNestedTests,
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'no-only-test': noOnlyTest,
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'ava/no-incorrect-deep-equal': 'error',
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'ava/no-inline-assertions': 'error',
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'ava/no-invalid-modifier-chain': 'error',
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'ava/no-negated-assertion': 'error',
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'ava/no-nested-assertions': 'error',
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'ava/no-nested-tests': 'error',
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'ava/no-only-test': 'error',

‎readme.md‎

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| [no-incorrect-deep-equal](docs/rules/no-incorrect-deep-equal.md) | Disallow using `deepEqual` with primitives. | ✅ | | | 🔧 | | |
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| [no-inline-assertions](docs/rules/no-inline-assertions.md) | Disallow inline assertions. | ✅ | | | 🔧 | | |
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| [no-invalid-modifier-chain](docs/rules/no-invalid-modifier-chain.md) | Disallow invalid modifier chains. | ✅ | | | 🔧 | 💡 | |
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| [no-negated-assertion](docs/rules/no-negated-assertion.md) | Disallow negated assertions. | ✅ | | | 🔧 | | |
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| [no-nested-assertions](docs/rules/no-nested-assertions.md) | Disallow nested assertions. | ✅ | | | | | |
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| [no-nested-tests](docs/rules/no-nested-tests.md) | Disallow nested tests. | ✅ | | | | | |
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| [no-only-test](docs/rules/no-only-test.md) | Disallow `test.only()`. | ✅ | | | | 💡 | |

‎rules/no-negated-assertion.js‎

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import {visitIf} from 'enhance-visitors';
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import util from '../util.js';
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import createAvaRule from '../create-ava-rule.js';
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const MESSAGE_ID = 'no-negated-assertion';
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const negatedPairs = {
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true: 'falsy',
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false: 'truthy',
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truthy: 'falsy',
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falsy: 'truthy',
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};
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const doubleNegatedPairs = {
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true: 'truthy',
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false: 'falsy',
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truthy: 'truthy',
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falsy: 'falsy',
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};
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const getArgumentText = (source, argument) => argument.type === 'SequenceExpression' ? `(${source.getText(argument)})` : source.getText(argument);
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const create = context => {
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const ava = createAvaRule();
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return ava.merge({
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CallExpression: visitIf([
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ava.isInTestFile,
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ava.isInTestNode,
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])(node => {
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if (node.callee.type !== 'MemberExpression') {
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return;
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}
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const root = util.getRootNode(node.callee);
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if (!util.isTestObject(root.object.name)) {
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return;
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}
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const members = util.getMembers(node.callee);
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const methodName = members[0];
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if (!negatedPairs[methodName]) {
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return;
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}
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if (!members.slice(1).every(member => member === 'skip')) {
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return;
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}
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const argument = node.arguments[0];
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if (!argument || argument.type !== 'UnaryExpression' || argument.operator !== '!') {
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return;
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}
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// Double negation: `t.true(!!x)` → `t.truthy(x)` to preserve behavior for non-boolean values.
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if (argument.argument.type === 'UnaryExpression' && argument.argument.operator === '!') {
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const replacement = doubleNegatedPairs[methodName];
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context.report({
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node,
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messageId: MESSAGE_ID,
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data: {
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assertion: methodName,
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replacement,
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},
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fix(fixer) {
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const source = context.sourceCode;
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return [
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fixer.replaceText(root.property, replacement),
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fixer.replaceText(argument, getArgumentText(source, argument.argument.argument)),
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];
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},
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});
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return;
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}
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const replacement = negatedPairs[methodName];
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context.report({
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node,
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messageId: MESSAGE_ID,
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data: {
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assertion: methodName,
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replacement,
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},
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fix(fixer) {
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const source = context.sourceCode;
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return [
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fixer.replaceText(root.property, replacement),
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fixer.replaceText(argument, getArgumentText(source, argument.argument)),
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];
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},
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});
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}),
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});
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};
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export default {
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create,
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meta: {
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type: 'suggestion',
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docs: {
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description: 'Disallow negated assertions.',
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recommended: true,
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url: util.getDocsUrl(import.meta.filename),
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},
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fixable: 'code',
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schema: [],
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messages: {
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[MESSAGE_ID]: 'Prefer `t.{{replacement}}()` over negating the argument of `t.{{assertion}}()`.',
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},
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},
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};

‎test/no-negated-assertion.js‎

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import RuleTester, {testCase} from './helpers/rule-tester.js';
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import rule from '../rules/no-negated-assertion.js';
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const ruleTester = new RuleTester();
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const errors = [{messageId: 'no-negated-assertion'}];
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ruleTester.run('no-negated-assertion', rule, {
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valid: [
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testCase('t.true(x)'),
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testCase('t.false(x)'),
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testCase('t.truthy(x)'),
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testCase('t.falsy(x)'),
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testCase('t.is(!x, y)'),
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testCase('t.assert(!x)'),
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testCase('t.true(x, "message")'),
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testCase('t.true()'),
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// Not a test object
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testCase('foo.true(!x)'),
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// `t.context` is not an assertion
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testCase('t.context.true(!x)'),
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// Invalid modifier order; handled by other rules
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testCase('t.skip.true(!x)'),
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// Invalid trailing member; handled by other rules
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testCase('t.true.context(!x)'),
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// Shouldn't be triggered since it's not a test file
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{code: testCase('t.true(!x)'), noHeader: true},
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],
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invalid: [
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{
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code: testCase('t.true(!x)'),
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output: testCase('t.falsy(x)'),
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errors,
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},
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{
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code: testCase('t.false(!x)'),
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output: testCase('t.truthy(x)'),
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errors,
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},
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{
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code: testCase('t.truthy(!x)'),
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output: testCase('t.falsy(x)'),
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errors,
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},
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{
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code: testCase('t.falsy(!x)'),
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output: testCase('t.truthy(x)'),
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errors,
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},
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// With message argument
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{
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code: testCase('t.true(!x, "msg")'),
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output: testCase('t.falsy(x, "msg")'),
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errors,
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},
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// Complex expressions
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{
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code: testCase('t.true(!foo.bar)'),
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output: testCase('t.falsy(foo.bar)'),
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errors,
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},
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{
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code: testCase('t.true(!foo())'),
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output: testCase('t.falsy(foo())'),
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errors,
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},
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{
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code: testCase('t.true(!(a === b))'),
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output: testCase('t.falsy(a === b)'),
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errors,
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},
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{
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code: testCase('t.true(!(a, b))'),
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output: testCase('t.falsy((a, b))'),
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errors,
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},
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// With .skip
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{
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code: testCase('t.true.skip(!x)'),
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output: testCase('t.falsy.skip(x)'),
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errors,
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},
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{
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code: testCase('t.truthy.skip(!x)'),
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output: testCase('t.falsy.skip(x)'),
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errors,
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},
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{
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code: testCase('t.true.skip.skip(!x)'),
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output: testCase('t.falsy.skip.skip(x)'),
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errors,
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},
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// Double negation
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{
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code: testCase('t.true(!!x)'),
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output: testCase('t.truthy(x)'),
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errors,
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},
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{
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code: testCase('t.false(!!x)'),
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output: testCase('t.falsy(x)'),
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errors,
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},
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{
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code: testCase('t.truthy(!!x)'),
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output: testCase('t.truthy(x)'),
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errors,
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},
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{
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code: testCase('t.true.skip(!!x)'),
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output: testCase('t.truthy.skip(x)'),
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errors,
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},
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{
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code: testCase('t.true(!!(a, b))'),
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output: testCase('t.truthy((a, b))'),
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errors,
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},
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// Non-boolean values
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{
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code: testCase('t.true(!0)'),
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output: testCase('t.falsy(0)'),
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errors,
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},
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{
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code: testCase('t.false(!0)'),
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output: testCase('t.truthy(0)'),
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errors,
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},
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{
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code: testCase('t.true(!!1)'),
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output: testCase('t.truthy(1)'),
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errors,
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},
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{
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code: testCase('t.false(!!1)'),
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output: testCase('t.falsy(1)'),
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errors,
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},
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// Alternative test object names
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{
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code: testCase('tt.true(!x)'),
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output: testCase('tt.falsy(x)'),
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errors,
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},
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],
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});

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