Add waitForAll method

Sources/AsyncAlgorithms/AsyncSquence.swift

@@ -0,0 +1,17 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift Async Algorithms open source project
+//
+// Copyright (c) 2022 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+//
+//===----------------------------------------------------------------------===//
+
+extension AsyncSequence where Element == Void {
+  /// Wait for an asynchronous sequence to complete.
+  public func waitForAll() async rethrows {
+    for try await _ in self {}
+  }
+}

Tests/AsyncAlgorithmsTests/TestAsyncSequence.swift

@@ -0,0 +1,29 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift Async Algorithms open source project
+//
+// Copyright (c) 2022 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+//
+//===----------------------------------------------------------------------===//
+
+import XCTest
+import AsyncAlgorithms
+
+final class TestAsyncSequence: XCTestCase {
+  func test_throwing_waitForAll() async throws {
+    let source = 1...5
+
+    let sequence = source.async.map {
+      _ = try throwOn(4, $0)
+      return ()
+    }
+    do {
+      try await sequence.waitForAll()
+    } catch {
+      XCTAssertTrue(error is Failure)
+    }
+  }
+}