# expect(throws:_:sourceLocation:performing:) Check that an expression always throws a specific error. ``` @discardableResult @freestanding(expression) macro expect(throws error: E, _ comment: @autoclosure () -> Comment? = nil, sourceLocation: SourceLocation = #_sourceLocation, performing expression: () async throws -> R) -> E? where E : Equatable, E : Error ``` ## Parameters `error` The error that is expected to be thrown. `comment` A comment describing the expectation. `sourceLocation` The source location to which recorded expectations and issues should be attributed. `expression` The expression to be evaluated. ## Return Value If the expectation passes, the instance of `E` that was thrown by `expression` and is equal to `error`. If the expectation fails, the result is `nil`. ## Overview Use this overload of `#expect()` when the expression `expression` *should* throw a specific error: ```swift #expect(throws: EngineFailureError.batteryDied) { FoodTruck.shared.engine.batteryLevel = 0 try FoodTruck.shared.engine.start() } ``` If `expression` does not throw an error, or if it throws an error that is not equal to `error`, an [`Issue`](/documentation/Testing/Issue) is recorded for the test that is running in the current task. Any value returned by `expression` is discarded. > Note: If you use this macro with a Swift compiler version lower than 6.1, > it doesn’t return a value. If the thrown error need only be an instance of a particular type, use [`expect(throws:_:sourceLocation:performing:)`](/documentation/Testing/expect(throws:_:sourceLocation:performing:)-1hfms) instead. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)