TestFoundation: add SPI for querying the thread name

This keeps the CoreFoundation interfaces confined to the Foundation
implementation and outside of the test suite.  This is needed to enable
tests on Windows.

Author: compnerd

Foundation/Thread.swift

@@ -255,6 +255,22 @@ open class Thread : NSObject {
         }
     }
 
+    internal var _name: String? {
+      var buf: [Int8] = Array<Int8>(repeating: 0, count: 128)
+      #if DEPLOYMENT_RUNTIME_OBJC
+        // Do not use _CF functions on the ObjC runtime as that breaks on the
+        // Darwin runtime.
+        if pthread_getname_np(pthread_self(), &buf, buf.count) == 0 {
+          return ""
+        }
+      #else
+        if _CFThreadGetName(&buf, Int32(buf.count)) == 0 {
+          return ""
+        }
+      #endif
+        return String(cString: buf)
+    }
+
 #if os(Windows)
     open var stackSize: Int {
       get {

TestFoundation/TestThread.swift

@@ -17,14 +17,22 @@ class TestThread : XCTestCase {
 #if os(Android)
         return []
 #endif
-        return [
+
+        var tests: [(String, (TestThread) -> () throws -> Void)] = [
             ("test_currentThread", test_currentThread ),
             ("test_threadStart", test_threadStart),
-            ("test_threadName", test_threadName),
             ("test_mainThread", test_mainThread),
             ("test_callStackSymbols", test_callStackSymbols),
             ("test_callStackReurnAddresses", test_callStackReturnAddresses),
         ]
+
+#if NS_FOUNDATION_ALLOWS_TESTABLE_IMPORT
+        tests.append(contentsOf: [
+            ("test_threadName", test_threadName),
+        ])
+#endif
+
+        return tests
     }
 
     func test_currentThread() {
@@ -50,31 +58,15 @@ class TestThread : XCTestCase {
         XCTAssertTrue(ok, "NSCondition wait timed out")
     }
 
+#if NS_FOUNDATION_ALLOWS_TESTABLE_IMPORT
     func test_threadName() {
-
-        // Compare the name set in pthreads()
-        func compareThreadName(to name: String) {
-            var buf = [Int8](repeating: 0, count: 128)
-#if os(macOS) || os(iOS)
-            // Don't use _CF functions on macOS as it will break testing with Darwin's native Foundation.
-            let r = pthread_getname_np(pthread_self(), &buf, buf.count)
-#else
-            let r = _CFThreadGetName(&buf, Int32(buf.count))
-#endif
-            if r == 0 {
-                XCTAssertEqual(String(cString: buf), name)
-            } else {
-                XCTFail("Cant get thread name")
-            }
-        }
-
         // No name is set initially
         XCTAssertNil(Thread.current.name)
 
 #if os(Linux) // Linux sets the initial thread name to the process name.
-        compareThreadName(to: "TestFoundation")
+        XCAssertEqual(Thread.current._name, "TestFoundation")
 #else
-        compareThreadName(to: "")
+        XCAssertEqual(Thread.current._name, "")
 #endif
         Thread.current.name = "mainThread"
         XCTAssertEqual(Thread.mainThread.name, "mainThread")
@@ -88,16 +80,16 @@ class TestThread : XCTestCase {
 
             Thread.current.name = "Thread2-2"
             XCTAssertEqual(Thread.current.name, "Thread2-2")
-            compareThreadName(to: "Thread2-2")
+            XCAssertEqual(Thread.current._name, Thread.current.name)
 
             Thread.current.name = "12345678901234567890"
             XCTAssertEqual(Thread.current.name, "12345678901234567890")
 #if os(macOS) || os(iOS)
-            compareThreadName(to: "12345678901234567890")
+            XCAssertEqual(Thread.current._name, Thread.current.name)
 #elseif os(Linux)
             // pthread_setname_np() only allows 15 characters on Linux, so setting it fails
             // and the previous name will still be there.
-            compareThreadName(to: "Thread2-2")
+            XCAssertEqual(Thread.current._name, "Thread2-2")
 #endif
             condition.lock()
             condition.signal()
@@ -116,6 +108,7 @@ class TestThread : XCTestCase {
         thread3.name = "Thread3"
         XCTAssertEqual(thread3.name, "Thread3")
     }
+#endif
 
     func test_mainThread() {
         XCTAssertTrue(Thread.isMainThread)