avajs/ava · error · AssertionError

The `name` property of the second argument to `${assertion}`

Error message

The `name` property of the second argument to `${assertion}` must be a string

What it means

This is an input-validation failure inside validateExpectations, the guard that checks the expectations object passed as the second argument to assertion helpers like t.throws() or t.notThrows(). It fires when expectations has a `name` key whose value is not a string (e.g. a number, object, or undefined), so the assertion cannot match it against an error's name. The assertion never runs; it is rejected up front as a misuse of the API, not as a failed assertion. Fix by passing expectations.name as a string.

Source

Thrown at lib/assert.js:118

				assertion,
				formattedDetails: [formatWithLabel('Called with:', expectations)],
			});
		}

		if (
			Object.hasOwn(expectations, 'message')
			&& typeof expectations.message !== 'string'
			&& !(expectations.message instanceof RegExp)
			&& !(typeof expectations.message === 'function')
		) {
			throw new AssertionError(`The \`message\` property of the second argument to \`${assertion}\` must be a string, regular expression or a function`, {
				assertion,
				formattedDetails: [formatWithLabel('Called with:', expectations)],
			});
		}

		if (Object.hasOwn(expectations, 'name') && typeof expectations.name !== 'string') {
			throw new AssertionError(`The \`name\` property of the second argument to \`${assertion}\` must be a string`, {
				assertion,
				formattedDetails: [formatWithLabel('Called with:', expectations)],
			});
		}

		if (Object.hasOwn(expectations, 'code') && typeof expectations.code !== 'string' && typeof expectations.code !== 'number') {
			throw new AssertionError(`The \`code\` property of the second argument to \`${assertion}\` must be a string or number`, {
				assertion,
				formattedDetails: [formatWithLabel('Called with:', expectations)],
			});
		}

		if (Object.hasOwn(expectations, 'any') && typeof expectations.any !== 'boolean') {
			throw new AssertionError(`The \`any\` property of the second argument to \`${assertion}\` must be a boolean`, {
				assertion,
				formattedDetails: [formatWithLabel('Called with:', expectations)],
			});
		}

View on GitHub (pinned to bbfd946322)

Solutions

1. Pass the name as a string, e.g. {name: 'RangeError'}
2. Read err.name from a sample error to get the exact string
3. Remove the name key if you meant to check the constructor via instanceOf

When it happens

Trigger: Thrown at lib/assert.js:118 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of avajs/ava@bbfd946322 (2026-09-02). Data as JSON: /api/errors/323b1fe31c5c8e2f. Report an issue: GitHub.