Add XCTest extension for testing async throwing expressions

Tests/SwiftPolyglotCoreTests/XCTest+AsyncThrowingExpression.swift

@@ -0,0 +1,77 @@
+import XCTest
+
+/// Asserts that an asynchronous expression do not throw an error.
+/// (Intended to function as a drop-in asynchronous version of `XCTAssertNoThrow`.)
+///
+/// Example usage:
+///
+///     await assertNoThrowAsync(
+///         try await sut.function()
+///     ) { error in
+///         XCTAssertEqual(error as? MyError, MyError.specificError)
+///     }
+///
+/// - Parameters:
+///   - expression: An asynchronous expression that can throw an error.
+///   - message: An optional description of a failure.
+///   - file: The file where the failure occurs. The default is the file path of the test case where this function is being called.
+///   - line: The line number where the failure occurs. The default is the line number where this function is being called.
+public func XCTAssertNoThrowAsync<T>(
+    _ expression: @autoclosure () async throws -> T,
+    _ message: @autoclosure () -> String = "",
+    file: StaticString = #filePath,
+    line: UInt = #line
+) async {
+    do {
+        _ = try await expression()
+    } catch {
+        // expected no error to be thrown, but it was
+        let customMessage = message()
+        if customMessage.isEmpty {
+            XCTFail("Asynchronous call did throw an error.", file: file, line: line)
+        } else {
+            XCTFail(customMessage, file: file, line: line)
+        }
+    }
+}
+
+/// Asserts that an asynchronous expression throws an error.
+/// (Intended to function as a drop-in asynchronous version of `XCTAssertThrowsError`.)
+///
+/// Example usage:
+///
+///     await assertThrowsAsyncError(
+///         try await sut.function()
+///     ) { error in
+///         XCTAssertEqual(error as? MyError, MyError.specificError)
+///     }
+///
+/// - Parameters:
+///   - expression: An asynchronous expression that can throw an error.
+///   - message: An optional description of a failure.
+///   - file: The file where the failure occurs. The default is the file path of the test case where this function is being called.
+///   - line: The line number where the failure occurs. The default is the line number where this function is being called.
+///   - errorHandler: An optional handler for errors that `expression` throws.
+///
+/// from: https://gitlab.com/-/snippets/2567566
+public func XCTAssertThrowsErrorAsync<T>(
+    _ expression: @autoclosure () async throws -> T,
+    _ message: @autoclosure () -> String = "",
+    file: StaticString = #filePath,
+    line: UInt = #line,
+    _ errorHandler: (_ error: any Error) -> Void = { _ in }
+) async {
+    do {
+        _ = try await expression()
+        // expected error to be thrown, but it was not
+        let customMessage = message()
+        if customMessage.isEmpty {
+            XCTFail("Asynchronous call did not throw an error.", file: file, line: line)
+        } else {
+            XCTFail(customMessage, file: file, line: line)
+        }
+    } catch {
+        errorHandler(error)
+    }
+}
+