Add a convenience method for creating in-process client/server (#1738)

Motivation:

To use the in-process transport users must create a server and then a
client depending on that server. It rarely makes sense to create one
without the other and I have written more or less the same extension in
three places to do this for me and return a pair. This should just be
made into API.

Modifications:

- Add a `InProcessTransport.makePair()` convenience method
- Replace use of old helpers

Result:

It's easier to create in-process transport.

Sources/GRPCInProcessTransport/InProcessTransport.swift

@@ -0,0 +1,43 @@
+/*
+ * Copyright 2023, gRPC Authors All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+import GRPCCore
+
+public enum InProcessTransport {
+  /// Returns a pair containing an ``InProcessServerTransport`` and an ``InProcessClientTransport``.
+  ///
+  /// This function is purely for convenience and does no more than constructing a server transport
+  /// and a client using that server transport.
+  ///
+  /// - Parameters:
+  ///   - methodConfiguration: Method specific configuration used by the client transport to
+  ///       determine how RPCs should be executed.
+  ///   - retryThrottle: The retry throttle the client transport uses to determine whether a call
+  ///       should be retried.
+  /// - Returns: A tuple containing the connected server and client in-process transports.
+  @available(macOS 13.0, iOS 16.0, watchOS 9.0, tvOS 16.0, *)
+  public static func makePair(
+    methodConfiguration: MethodConfigurations = MethodConfigurations(),
+    retryThrottle: RetryThrottle? = nil
+  ) -> (server: InProcessServerTransport, client: InProcessClientTransport) {
+    let server = InProcessServerTransport()
+    let client = InProcessClientTransport(
+      server: server,
+      methodConfiguration: methodConfiguration,
+      retryThrottle: retryThrottle
+    )
+    return (server, client)
+  }
+}

Tests/GRPCCoreTests/GRPCClientTests.swift

@@ -20,22 +20,12 @@ import XCTest
 
 @available(macOS 13.0, iOS 16.0, watchOS 9.0, tvOS 16.0, *)
 final class GRPCClientTests: XCTestCase {
-  func makeInProcessPair() -> (client: InProcessClientTransport, server: InProcessServerTransport) {
-    let server = InProcessServerTransport()
-    let client = InProcessClientTransport(
-      server: server,
-      methodConfiguration: MethodConfigurations()
-    )
-
-    return (client, server)
-  }
-
   func withInProcessConnectedClient(
     services: [any RegistrableRPCService],
     interceptors: [any ClientInterceptor] = [],
     _ body: (GRPCClient, GRPCServer) async throws -> Void
   ) async throws {
-    let inProcess = self.makeInProcessPair()
+    let inProcess = InProcessTransport.makePair()
     let client = GRPCClient(transport: inProcess.client, interceptors: interceptors)
     let server = GRPCServer(transports: [inProcess.server], services: services)
 
@@ -325,7 +315,7 @@ final class GRPCClientTests: XCTestCase {
   }
 
   func testCancelRunningClient() async throws {
-    let inProcess = self.makeInProcessPair()
+    let inProcess = InProcessTransport.makePair()
     let client = GRPCClient(transport: inProcess.client)
 
     try await withThrowingTaskGroup(of: Void.self) { group in
@@ -374,7 +364,7 @@ final class GRPCClientTests: XCTestCase {
   }
 
   func testRunStoppedClient() async throws {
-    let (clientTransport, _) = self.makeInProcessPair()
+    let (_, clientTransport) = InProcessTransport.makePair()
     let client = GRPCClient(transport: clientTransport)
     // Run the client.
     let task = Task { try await client.run() }
@@ -390,7 +380,7 @@ final class GRPCClientTests: XCTestCase {
   }
 
   func testRunAlreadyRunningClient() async throws {
-    let (clientTransport, _) = self.makeInProcessPair()
+    let (_, clientTransport) = InProcessTransport.makePair()
     let client = GRPCClient(transport: clientTransport)
     // Run the client.
     let task = Task { try await client.run() }

Tests/GRPCCoreTests/GRPCServerTests.swift

@@ -20,19 +20,12 @@ import XCTest
 
 @available(macOS 13.0, iOS 16.0, watchOS 9.0, tvOS 16.0, *)
 final class GRPCServerTests: XCTestCase {
-  func makeInProcessPair() -> (client: InProcessClientTransport, server: InProcessServerTransport) {
-    let server = InProcessServerTransport()
-    let client = InProcessClientTransport(server: server)
-
-    return (client, server)
-  }
-
   func withInProcessClientConnectedToServer(
     services: [any RegistrableRPCService],
     interceptors: [any ServerInterceptor] = [],
     _ body: (InProcessClientTransport, GRPCServer) async throws -> Void
   ) async throws {
-    let inProcess = self.makeInProcessPair()
+    let inProcess = InProcessTransport.makePair()
     let server = GRPCServer(
       transports: [inProcess.server],
       services: services,
@@ -298,7 +291,7 @@ final class GRPCServerTests: XCTestCase {
   }
 
   func testCancelRunningServer() async throws {
-    let inProcess = self.makeInProcessPair()
+    let inProcess = InProcessTransport.makePair()
     let task = Task {
       let server = GRPCServer(transports: [inProcess.server], services: [BinaryEcho()])
       try await server.run()
@@ -353,7 +346,8 @@ final class GRPCServerTests: XCTestCase {
 
   func testRunServerDrainsRunningTransportsWhenOneFailsToStart() async throws {
     // Register the in process transport first and allow it to come up.
-    let inProcess = self.makeInProcessPair()
+    let inProcess = InProcessTransport.makePair()
+
     // Register a transport waits for a signal before throwing.
     let signal = AsyncStream.makeStream(of: Void.self)
     let server = GRPCServer(