avajs/ava · error · TypeError

`t.try()` titles must be strings

Error message

`t.try()` titles must be strings

What it means

The optional title given to t.try() must be a string. AVA parses the title from the arguments; if a non-string truthy value is passed in the title position (e.g. a number or object) and it cannot be interpreted as a valid title, this TypeError is thrown.

Source

Thrown at lib/test.js:114

			if (test.isHook) {
				const error = new Error('`t.try()` can only be used in tests');
				test.saveFirstError(error);
				throw error;
			}

			const {args, implementation, title} = parseTestArgs(attemptArgs);

			if (typeof implementation !== 'function') {
				throw new TypeError('Expected an implementation.');
			}

			let attemptTitle;
			if (!title.isSet || title.isEmpty) {
				attemptTitle = `${test.title} ─ attempt ${test.attemptCount + 1}`;
			} else if (title.isValid) {
				attemptTitle = `${test.title} ─ ${title.value}`;
			} else {
				throw new TypeError('`t.try()` titles must be strings');
			}

			if (!test.registerUniqueTitle(attemptTitle)) {
				throw new Error(`Duplicate test title: ${attemptTitle}`);
			}

			let committed = false;
			let discarded = false;

			const {assertCount, deferredSnapshotRecordings, errors, logs, passed, snapshotCount, startingSnapshotCount} = await test.runAttempt(attemptTitle, t => implementation(t, ...args));

			return {
				errors,
				logs: [...logs], // Don't allow modification of logs.
				passed,
				title: attemptTitle,
				commit({retainLogs = true} = {}) {
					if (committed) {

View on GitHub (pinned to bbfd946322)

Solutions

1. Pass the title as a string: t.try('my title', impl).
2. Remove the title entirely and let AVA generate 'attempt N' automatically.
3. Add a type check or TypeScript annotation so the title is always string.

Example fix

// before
const attempt = t.try(123, impl);

// after
const attempt = t.try('attempt 123', impl);

if (title !== undefined && typeof title !== 'string') throw new TypeError('t.try() title must be a string');

const isValidTitle = (v) => v === undefined || typeof v === 'string';

When it happens

Trigger: t.try(42, impl) or t.try({label: 'x'}, impl) — a non-string first argument that is not a function; passing a title that is not a string or a function in the t.try(title, implementation, ...args) overload.

Common situations: Using template variables that resolved to a number; copying macros that accept titles as objects; TypeScript projects where `any` suppressed the type error until runtime.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• Expected an implementation.
• Expected an implementation. Use `test.todo()` for tests with
• Test & hook titles must be strings
• Tests must have a title
• Cannot record snapshot ${index} for ${JSON.stringify(belongs

AI-assisted analysis of avajs/ava@bbfd946322 (2026-09-02). Data as JSON: /api/errors/1591451a07587576. Report an issue: GitHub.