Make AsyncShellTask.finish return self.

For method chaining.

SwiftShell/Command.swift

@@ -121,13 +121,15 @@ public struct AsyncShellTask {
 	/** 
    Wait for this shell task to finish.
 
+   - returns: itself
    - throws: a ShellError if the return code is anything but 0.
 	*/
-	public func finish() throws {
+	public func finish() throws -> AsyncShellTask {
 		task.waitUntilExit()
-		if task.terminationStatus != 0 {
+		guard task.terminationStatus == 0 else {
 			throw ShellError.ReturnedErrorCode(errorcode: task.terminationStatus)
 		}
+		return self
 	}
 }
 

SwiftShellTests/Command_Tests.swift

@@ -50,4 +50,11 @@ class RunAsync_Tests: XCTestCase {
 		AssertThrows(ShellError.ReturnedErrorCode(errorcode: 1)) { try asynctask.finish() }
 		XCTAssertEqual( asynctask.stderror.read(), "errormessage\n" )
 	}
+
+	func testFinishReturnsSelf () {
+		AssertNoThrow {
+			let output = try main.runAsync(bash: "echo hi").finish().stdout.read()
+			XCTAssertEqual(output, "hi\n")
+		}
+	}
 }