diff --git a/src/BizHawk.Tests/Common/NumberExtensions/NumberExtensionsTests.cs b/src/BizHawk.Tests/Common/NumberExtensions/NumberExtensionsTests.cs
new file mode 100644
index 0000000000..d5d32304ea
--- /dev/null
+++ b/src/BizHawk.Tests/Common/NumberExtensions/NumberExtensionsTests.cs
@@ -0,0 +1,33 @@
+using NE = BizHawk.Common.NumberExtensions.NumberExtensions;
+
+namespace BizHawk.Tests.Common.NumberExtensions
+{
+	[TestClass]
+	public class StringExtensionTests
+	{
+		[DataRow(int.MinValue, -1)]
+		[DataRow(-1, -1)]
+		[DataRow(0, -1)]
+		[DataRow(1, 0)]
+		[DataRow(2, 0)]
+		[DataRow(9, 0)]
+		[DataRow(10, 1)]
+		[DataRow(11, 1)]
+		[DataRow(99, 1)]
+		[DataRow(100, 2)]
+		[DataRow(101, 2)]
+		[DataRow(999, 2)]
+		[DataRow(1000, 3)]
+		[DataRow(1001, 3)]
+		[DataRow(9999, 3)]
+		[DataRow(10000, 4)]
+		[DataRow(10001, 4)]
+		[TestMethod]
+		public void TestLog10(int input, int expected)
+		{
+			var actual = NE.Log10(input);
+			Assert.AreEqual(expected, actual, "should match docs");
+			if (expected >= 0) Assert.AreEqual(unchecked((int) Math.Log10(input)), actual, "should match BCL");
+		}
+	}
+}