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prefer-comparison-matcher.ts
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prefer-comparison-matcher.ts
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import { AST_NODE_TYPES, type TSESTree } from '@typescript-eslint/utils';
import {
EqualityMatcher,
createRule,
getAccessorValue,
getFirstMatcherArg,
getSourceCode,
isBooleanLiteral,
isStringNode,
parseJestFnCall,
} from './utils';
const isString = (node: TSESTree.Node) => {
return isStringNode(node) || node.type === AST_NODE_TYPES.TemplateLiteral;
};
const isComparingToString = (expression: TSESTree.BinaryExpression) => {
return isString(expression.left) || isString(expression.right);
};
const invertOperator = (operator: string) => {
switch (operator) {
case '>':
return '<=';
case '<':
return '>=';
case '>=':
return '<';
case '<=':
return '>';
}
return null;
};
const determineMatcher = (
operator: string,
negated: boolean,
): string | null => {
const op = negated ? invertOperator(operator) : operator;
switch (op) {
case '>':
return 'toBeGreaterThan';
case '<':
return 'toBeLessThan';
case '>=':
return 'toBeGreaterThanOrEqual';
case '<=':
return 'toBeLessThanOrEqual';
}
return null;
};
export default createRule({
name: __filename,
meta: {
docs: {
category: 'Best Practices',
description: 'Suggest using the built-in comparison matchers',
recommended: false,
},
messages: {
useToBeComparison: 'Prefer using `{{ preferredMatcher }}` instead',
},
fixable: 'code',
type: 'suggestion',
schema: [],
},
defaultOptions: [],
create(context) {
return {
CallExpression(node) {
const jestFnCall = parseJestFnCall(node, context);
if (jestFnCall?.type !== 'expect' || jestFnCall.args.length === 0) {
return;
}
const { parent: expect } = jestFnCall.head.node;
if (expect?.type !== AST_NODE_TYPES.CallExpression) {
return;
}
const {
arguments: [comparison],
range: [, expectCallEnd],
} = expect;
const { matcher } = jestFnCall;
const matcherArg = getFirstMatcherArg(jestFnCall);
if (
comparison?.type !== AST_NODE_TYPES.BinaryExpression ||
isComparingToString(comparison) ||
!EqualityMatcher.hasOwnProperty(getAccessorValue(matcher)) ||
!isBooleanLiteral(matcherArg)
) {
return;
}
const [modifier] = jestFnCall.modifiers;
const hasNot = jestFnCall.modifiers.some(
nod => getAccessorValue(nod) === 'not',
);
const preferredMatcher = determineMatcher(
comparison.operator,
matcherArg.value === hasNot,
);
if (!preferredMatcher) {
return;
}
context.report({
fix(fixer) {
const sourceCode = getSourceCode(context);
// preserve the existing modifier if it's not a negation
const modifierText =
modifier && getAccessorValue(modifier) !== 'not'
? `.${getAccessorValue(modifier)}`
: '';
return [
// replace the comparison argument with the left-hand side of the comparison
fixer.replaceText(
comparison,
sourceCode.getText(comparison.left),
),
// replace the current matcher & modifier with the preferred matcher
fixer.replaceTextRange(
[expectCallEnd, matcher.parent.range[1]],
`${modifierText}.${preferredMatcher}`,
),
// replace the matcher argument with the right-hand side of the comparison
fixer.replaceText(
matcherArg,
sourceCode.getText(comparison.right),
),
];
},
messageId: 'useToBeComparison',
data: { preferredMatcher },
node: matcher,
});
},
};
},
});