oxc-project/oxc · error

Expect must have a corresponding matcher call.

Error message

Expect must have a corresponding matcher call.

What it means

Diagnostic from the oxlint `jest/valid-expect` rule (source: crates/oxc_linter/src/rules/shared/jest_vitest/valid_expect.rs:23). This message ('Expect must have a corresponding matcher call.') fires when `expect(value)` is never chained to a matcher - the expression's value is discarded, so the assertion never runs and the test passes vacuously. The rule uses `ExpectError`-style helpers and the shared diagnostic builder in the source.

Source

Thrown at crates/oxc_linter/src/rules/shared/jest_vitest/valid_expect.rs:23

use oxc_semantic::ScopeId;
use oxc_span::{GetSpan, Span};
use rustc_hash::FxHashSet;
use schemars::JsonSchema;

use crate::{
    AstNode,
    context::LintContext,
    utils::{
        ExpectError, PossibleJestNode, collect_possible_jest_call_node, parse_expect_jest_fn_call,
    },
};

fn valid_expect_diagnostic<S: Into<Cow<'static, str>>>(
    x1: S,
    x2: &'static str,
    span3: Span,
) -> OxcDiagnostic {
    OxcDiagnostic::warn(x1).with_help(x2).with_label(span3)
}

pub const DOCUMENTATION: &str = r"### What it does

Checks that `expect()` is called correctly.

### Why is this bad?

`expect()` is a function that is used to assert values in tests.
It should be called with a single argument, which is the value to be tested.
If you call `expect()` with no arguments, or with more than one argument, it will not work as expected.

### Examples

Examples of **incorrect** code for this rule:
```javascript
expect();
expect('something');

View on GitHub (pinned to e1e7af627c)

Solutions

1. Complete the assertion: `expect(value).toBe(expected)` or whichever matcher applies.
2. If the line was a debugging leftover, delete the bare `expect(...)`.
3. For promise assertions use the full chain: `await expect(fetchUser()).resolves.toMatchObject({ id: 1 })`.
4. Search for the pattern repo-wide with `rg 'expect\([^)]*\);\s*$'` to catch other occurrences.

Example fix

// before
expect(result.status);

// after
expect(result.status).toBe('ok');

// rg -n "expect\([^)]*\);\s*$" tests/ -t ts -t js  # bare expect statements

// Guard for dynamic assertion helpers (JS):
function assertHasMatcher(fn) {
  const src = fn.toString();
  return !/^\s*expect\([^)]*\);\s*$/m.test(src);
}

When it happens

Trigger: `expect(value);` as a standalone expression statement, `const p = expect(x);` never followed by `.toBe/...`, or an expect chain broken by a stray semicolon or early return before the matcher. Detected via `collect_possible_jest_call_node` + `parse_expect_jest_fn_call` finding no matcher.

Common situations: Commenting out a matcher while debugging and forgetting to restore it; refactors that split the chain across lines; await-less `expect(promise).resolves...` typos where the chain got truncated; copy-paste that dropped the second line.

Related errors

• Matchers must be called to assert.
• Expect has an unknown modifier.
• Async assertions must be awaited.
• Promises which return async assertions must be awaited.
• Expect takes at most {} argument{}

AI-assisted analysis of oxc-project/oxc@e1e7af627c (2026-08-20). Data as JSON: /api/errors/c085f4d899c1fe6e. Report an issue: GitHub.