Apply suggestions from code review

This better communicates the intention.

Co-authored-by: loffgren <[email protected]>

Author: glessard

Tests/SystemTests/MachPortTests.swift

@@ -188,23 +188,15 @@ final class MachPortTests: XCTestCase {
         let recv = Mach.Port<Mach.ReceiveRight>()
         let send = recv.makeSendRight()
         _ = consume recv // and turn `send` into a dead name
-        do {
-            let copy = try send.copySendRight()
-            _ = copy
-        }
-        catch Mach.PortRightError.deadName {
-          // success
+        XCTAssertThrowsError(try send.copySendRight(), "Copying a dead name should throw") { error in
+            XCTAssertEqual(error, Mach.PortRightError.deadName)
         }
     }
 
     func testCopyDeadName2() throws {
         let send = Mach.Port<Mach.SendRight>(name: 0xffffffff)
-        do {
-            let copy = try send.copySendRight()
-            _ = copy
-        }
-        catch Mach.PortRightError.deadName {
-          // success
+        XCTAssertThrowsError(try send.copySendRight(), "Copying a dead name should throw") { error in
+            XCTAssertEqual(error, Mach.PortRightError.deadName)
         }
     }