From 0b756e4e7f3f09fbe20cb5c2f1c47249cb3171dc Mon Sep 17 00:00:00 2001
From: Brian Rogers <bobbymcr@gmail.com>
Date: Sun, 9 Feb 2020 21:39:11 -0800
Subject: [PATCH] DirectoryWatcherBase - SubscribeNullFile

---
 .../DirectoryWatcherBase.cs                          |  5 +++++
 .../DirectoryWatcherBaseTest.cs                      | 12 ++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/projects/DirectoryWatcherSample/DirectoryWatcherSample.Core/DirectoryWatcherBase.cs b/projects/DirectoryWatcherSample/DirectoryWatcherSample.Core/DirectoryWatcherBase.cs
index 7001eaf..011de46 100644
--- a/projects/DirectoryWatcherSample/DirectoryWatcherSample.Core/DirectoryWatcherBase.cs
+++ b/projects/DirectoryWatcherSample/DirectoryWatcherSample.Core/DirectoryWatcherBase.cs
@@ -26,6 +26,11 @@ protected DirectoryWatcherBase(DirectoryInfo path)
 
         public IDisposable Subscribe(string file, Action<FileInfo> onUpdate)
         {
+            if (file == null)
+            {
+                throw new ArgumentNullException(nameof(file));
+            }
+
             FileInfo fullPath = new FileInfo(Path.Combine(this.path, file));
             string key = fullPath.FullName;
             Action onDispose = () => this.subscriptions.TryRemove(key, out _);
diff --git a/projects/DirectoryWatcherSample/DirectoryWatcherSample.Test/DirectoryWatcherBaseTest.cs b/projects/DirectoryWatcherSample/DirectoryWatcherSample.Test/DirectoryWatcherBaseTest.cs
index ad52bdc..eceb401 100644
--- a/projects/DirectoryWatcherSample/DirectoryWatcherSample.Test/DirectoryWatcherBaseTest.cs
+++ b/projects/DirectoryWatcherSample/DirectoryWatcherSample.Test/DirectoryWatcherBaseTest.cs
@@ -177,6 +177,18 @@ public void SubscribeSameFileTwiceDifferentCase()
                 .WithMessage(@"A subscription for 'X:\root\FILE1.txt' already exists.");
         }
 
+        [TestMethod]
+        public void SubscribeNullFile()
+        {
+            DirectoryWatcherBase watcherBase = new FakeDirectoryWatcher(new DirectoryInfo(@"X:\root"));
+            Action<FileInfo> onUpdate = f => { };
+            string file = null;
+
+            Action act = () => watcherBase.Subscribe(file, onUpdate);
+
+            act.Should().Throw<ArgumentNullException>().Which.ParamName.Should().Be("file");
+        }
+
         private sealed class FakeDirectoryWatcher : DirectoryWatcherBase
         {
             public FakeDirectoryWatcher(DirectoryInfo path)