diff --git a/src/Test/L0/HostContextL0.cs b/src/Test/L0/HostContextL0.cs
index 40841a301..73fc32065 100644
--- a/src/Test/L0/HostContextL0.cs
+++ b/src/Test/L0/HostContextL0.cs
@@ -1,7 +1,9 @@
 using GitHub.Runner.Common.Util;
+using System;
 using System.IO;
 using System.Reflection;
 using System.Runtime.CompilerServices;
+using System.Text;
 using System.Threading;
 using Xunit;
 
@@ -67,6 +69,44 @@ namespace GitHub.Runner.Common.Tests
             }
         }
 
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Common")]
+        public void DefaultSecretMaskers()
+        {
+            try
+            {
+                // Arrange.
+                Setup();
+
+                // Act.
+                _hc.SecretMasker.AddValue("Password123!");
+                _hc.SecretMasker.AddValue("Pass\"word\"123!");
+                _hc.SecretMasker.AddValue("Pass word 123!");
+                _hc.SecretMasker.AddValue("Pass<word>123!");
+                _hc.SecretMasker.AddValue("Pass'word'123!");
+
+                // Assert.
+                Assert.Equal("123***123", _hc.SecretMasker.MaskSecrets("123Password123!123"));
+                Assert.Equal("password123", _hc.SecretMasker.MaskSecrets("password123"));
+                Assert.Equal("123***123", _hc.SecretMasker.MaskSecrets("123Pass\\\"word\\\"123!123"));
+                Assert.Equal("123***123", _hc.SecretMasker.MaskSecrets("123Pass%20word%20123%21123"));
+                Assert.Equal("123***123", _hc.SecretMasker.MaskSecrets("123Pass&lt;word&gt;123!123"));
+                Assert.Equal("123***123", _hc.SecretMasker.MaskSecrets("123Pass''word''123!123"));
+                Assert.Equal("OlBh***", _hc.SecretMasker.MaskSecrets(Convert.ToBase64String(Encoding.UTF8.GetBytes($":Password123!"))));
+                Assert.Equal("YTpQ***", _hc.SecretMasker.MaskSecrets(Convert.ToBase64String(Encoding.UTF8.GetBytes($"a:Password123!"))));
+                Assert.Equal("YWI6***", _hc.SecretMasker.MaskSecrets(Convert.ToBase64String(Encoding.UTF8.GetBytes($"ab:Password123!"))));
+                Assert.Equal("YWJjOlBh***", _hc.SecretMasker.MaskSecrets(Convert.ToBase64String(Encoding.UTF8.GetBytes($"abc:Password123!"))));
+                Assert.Equal("YWJjZDpQ***", _hc.SecretMasker.MaskSecrets(Convert.ToBase64String(Encoding.UTF8.GetBytes($"abcd:Password123!"))));
+                Assert.Equal("YWJjZGU6***", _hc.SecretMasker.MaskSecrets(Convert.ToBase64String(Encoding.UTF8.GetBytes($"abcde:Password123!"))));
+            }
+            finally
+            {
+                // Cleanup.
+                Teardown();
+            }
+        }
+
         public void Setup([CallerMemberName] string testName = "")
         {
             _tokenSource = new CancellationTokenSource();