test: Fix potential deadlock in TestLogOutput (#5617)

The test testLoggingFromMultipleThreads lead to deadlocks. This is fixed
now by using a NSLock instead of a DispatchQueue. This PR also makes the
logsToConsole immutable and adds more tests.

Author: philipphofmann

Tests/SentryTests/TestLogOutput.swift

@@ -4,14 +4,16 @@ import XCTest
 
 final class TestLogOutput {
 
-    private let queue = DispatchQueue(label: "TestLogOutput", attributes: .concurrent)
-    
+    private let logsToConsole: Bool
     private var _loggedMessages: [String] = []
-    
-    var logsToConsole: Bool = true
+    private let lock = NSLock()
+
+    init(logsToConsole: Bool = true) {
+        self.logsToConsole = logsToConsole
+    }
 
     var loggedMessages: [String] {
-        queue.sync {
+        lock.synchronized {
             return _loggedMessages
         }
     }
@@ -20,21 +22,116 @@ final class TestLogOutput {
         if logsToConsole {
             print(message)
         }
-        queue.async(flags: .barrier) {
+        lock.synchronized {
             self._loggedMessages.append(message)
         }
     }
 }
 
 class TestLogOutPutTests: XCTestCase {
 
-    func testLoggingFromMulitpleThreads() {
-        let sut = TestLogOutput()
-        sut.logsToConsole = false
-        testConcurrentModifications(writeWork: { i in
-            sut.log("Some message \(i)")
-        }, readWork: {
-            XCTAssertNotNil(sut.loggedMessages)
-        })
+    func testLoggingFromMultipleThreads() {
+        // Arrange
+        let sut = TestLogOutput(logsToConsole: false)
+
+        let queue = DispatchQueue(label: "testLoggingFromMultipleThreads", attributes: [.concurrent])
+        let expectation = expectation(description: "Logging from multiple threads")
+
+        let iterations = 100
+        expectation.expectedFulfillmentCount = iterations * 2
+
+        // Act
+        for i in 0..<iterations {
+
+            queue.async {
+                sut.log("Message \(i)")
+                expectation.fulfill()
+            }
+
+            queue.async {
+                XCTAssertNotNil(sut.loggedMessages)
+                expectation.fulfill()
+            }
+        }
+
+        wait(for: [expectation], timeout: 5.0)
+
+        // Assert
+        XCTAssertEqual(sut.loggedMessages.count, iterations)
+    }
+    
+    func testInitialState_LoggedMessagesIsEmpty() {
+        // Arrange
+        let sut = TestLogOutput(logsToConsole: false)
+        
+        // Act
+        let messages = sut.loggedMessages
+        
+        // Assert
+        XCTAssertTrue(messages.isEmpty)
+        XCTAssertEqual(messages.count, 0)
+    }
+    
+    func testLogSingleMessage_MessageIsStored() {
+        // Arrange
+        let sut = TestLogOutput(logsToConsole: false)
+        let testMessage = "Test message"
+        
+        // Act
+        sut.log(testMessage)
+        
+        // Assert
+        let messages = sut.loggedMessages
+        XCTAssertEqual(messages.count, 1)
+        XCTAssertEqual(messages.first, testMessage)
+    }
+    
+    func testLogMultipleMessages_AllMessagesAreStoredInOrder() {
+        // Arrange
+        let sut = TestLogOutput(logsToConsole: false)
+        let testMessages = ["First message", "Second message", "Third message"]
+        
+        // Act
+        for message in testMessages {
+            sut.log(message)
+        }
+        
+        // Assert
+        let messages = sut.loggedMessages
+        XCTAssertEqual(messages.count, testMessages.count)
+        XCTAssertEqual(messages, testMessages)
+    }
+    
+    func testLogEmptyString_EmptyStringIsStored() {
+        // Arrange
+        let sut = TestLogOutput(logsToConsole: false)
+        let emptyMessage = ""
+        
+        // Act
+        sut.log(emptyMessage)
+        
+        // Assert
+        let messages = sut.loggedMessages
+        XCTAssertEqual(messages.count, 1)
+        XCTAssertEqual(messages.first, emptyMessage)
+    }
+    
+    func testLogAfterMultipleReads_MessagesAreConsistent() {
+        // Arrange
+        let sut = TestLogOutput(logsToConsole: false)
+        let firstMessage = "First message"
+        let secondMessage = "Second message"
+        
+        // Act
+        sut.log(firstMessage)
+        let messagesAfterFirst = sut.loggedMessages
+        sut.log(secondMessage)
+        let messagesAfterSecond = sut.loggedMessages
+        
+        // Assert
+        XCTAssertEqual(messagesAfterFirst.count, 1)
+        XCTAssertEqual(messagesAfterFirst.first, firstMessage)
+        XCTAssertEqual(messagesAfterSecond.count, 2)
+        XCTAssertEqual(messagesAfterSecond, [firstMessage, secondMessage])
     }
 }