public FileLogHandler(string filePath, bool overwrite)
 {
+    if (string.IsNullOrEmpty(filePath)) throw new ArgumentException("File log path cannot be null or empty.", nameof(filePath));
 

-_fileStream = File.Open(filePath, fileMode, FileAccess.Write, FileShare.Read);
+_fileStream = File.Open(filePath, fileMode, FileAccess.Write, overwrite ? FileShare.None : FileShare.Read);
 

-public void ShouldAppendFileIfDoesNotExist()
+public void ShouldCreateAndAppendFileIfDoesNotExist()
 

+var initialSize = new FileInfo(tempFile).Length;
 using (var fileLogHandler = new FileLogHandler(tempFile, overwrite: true))
 {
     fileLogHandler.Handle(new LogEvent(typeof(FileLogHandlerTest), DateTimeOffset.Now, LogEventLevel.Info, "test message"));
 }
+var finalSize = new FileInfo(tempFile).Length;
+Assert.That(finalSize, Is.LessThanOrEqualTo(initialSize));
 Assert.That(Regex.Matches(File.ReadAllText(tempFile), "test message").Count, Is.EqualTo(1));
 

-var tempFile = Path.GetTempFileName();
-try
+[SetUp]
+public void Setup()
+{
+    tempFile = Path.GetTempFileName();
+}
+
+[TearDown]
+public void Teardown()
+{
+    File.Delete(tempFile);
+}
+
+[Test]
+public void ShouldAppendFileIfExists()
 {
     using (var fileLogHandler = new FileLogHandler(tempFile))
     {
         fileLogHandler.Handle(new LogEvent(typeof(FileLogHandlerTest), DateTimeOffset.Now, LogEventLevel.Info, "test message"));
     }
     using (var fileLogHandler2 = new FileLogHandler(tempFile))
     {
         fileLogHandler2.Handle(new LogEvent(typeof(FileLogHandlerTest), DateTimeOffset.Now, LogEventLevel.Info, "test message"));
     }
     Assert.That(Regex.Matches(File.ReadAllText(tempFile), "test message").Count, Is.EqualTo(2));
 }
-finally
-{
-    File.Delete(tempFile);
-}