diff --git a/SafeExamBrowser.Configuration.UnitTests/SafeExamBrowser.Configuration.UnitTests.csproj b/SafeExamBrowser.Configuration.UnitTests/SafeExamBrowser.Configuration.UnitTests.csproj
index 4d9e254a..de04bb25 100644
--- a/SafeExamBrowser.Configuration.UnitTests/SafeExamBrowser.Configuration.UnitTests.csproj
+++ b/SafeExamBrowser.Configuration.UnitTests/SafeExamBrowser.Configuration.UnitTests.csproj
@@ -96,6 +96,7 @@
     <Compile Include="DataFormats\XmlParserTests.cs" />
     <Compile Include="DataFormats\XmlSerializerTests.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
+    <Compile Include="SubStreamTests.cs" />
   </ItemGroup>
   <ItemGroup>
     <None Include="app.config" />
diff --git a/SafeExamBrowser.Configuration.UnitTests/SubStreamTests.cs b/SafeExamBrowser.Configuration.UnitTests/SubStreamTests.cs
new file mode 100644
index 00000000..6e6b83f8
--- /dev/null
+++ b/SafeExamBrowser.Configuration.UnitTests/SubStreamTests.cs
@@ -0,0 +1,186 @@
+/*
+ * Copyright (c) 2019 ETH Zürich, Educational Development and Technology (LET)
+ * 
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+using System;
+using System.IO;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Moq;
+
+namespace SafeExamBrowser.Configuration.UnitTests
+{
+	[TestClass]
+	public class SubStreamTests
+	{
+		private Mock<Stream> stream;
+
+		[TestInitialize]
+		public void Initialize()
+		{
+			stream = new Mock<Stream>();
+
+			stream.SetupGet(s => s.CanRead).Returns(true);
+			stream.SetupGet(s => s.CanSeek).Returns(true);
+			stream.SetupGet(s => s.Length).Returns(1000);
+		}
+
+		[TestMethod]
+		public void MustSetPropertiesCorrectly()
+		{
+			var sut = new SubStream(stream.Object, 100, 200);
+
+			Assert.IsTrue(sut.CanRead);
+			Assert.IsTrue(sut.CanSeek);
+			Assert.IsFalse(sut.CanWrite);
+			Assert.AreEqual(200, sut.Length);
+			Assert.AreEqual(0, sut.Position);
+		}
+
+		[TestMethod]
+		public void MustReadCorrectly()
+		{
+			var position = 750L;
+			var sut = new SubStream(stream.Object, 100, 200);
+
+			stream.SetupGet(s => s.Position).Returns(position);
+			stream.SetupSet(s => s.Position = It.IsAny<long>()).Callback<long>(p => position = p);
+			stream.Setup(s => s.Read(It.IsAny<byte[]>(), It.IsAny<int>(), It.IsAny<int>())).Returns<byte[], int, int>((a, o, c) => c);
+			sut.Position = 50;
+
+			var bytesRead = sut.Read(new byte[25], 0, 25);
+
+			stream.Verify(s => s.Read(It.IsAny<byte[]>(), 0, 25), Times.Once);
+
+			Assert.AreEqual(25, bytesRead);
+			Assert.AreEqual(75, sut.Position);
+			Assert.AreEqual(750, position);
+
+			sut.Position = 150;
+			bytesRead = sut.Read(new byte[75], 0, 75);
+
+			stream.Verify(s => s.Read(It.IsAny<byte[]>(), 0, 50), Times.Once);
+
+			Assert.AreEqual(50, bytesRead);
+			Assert.AreEqual(200, sut.Position);
+			Assert.AreEqual(750, position);
+		}
+
+		[TestMethod]
+		public void MustNotReadOutsideOfBounds()
+		{
+			var sut = new SubStream(stream.Object, 100, 200);
+
+			sut.Position = -1;
+
+			var bytesRead = sut.Read(new byte[0], 0, 0);
+
+			Assert.AreEqual(0, bytesRead);
+			stream.Verify(s => s.ReadByte(), Times.Never);
+			stream.Verify(s => s.Read(It.IsAny<byte[]>(), It.IsAny<int>(), It.IsAny<int>()), Times.Never);
+
+			sut.Position = 500;
+			bytesRead = sut.Read(new byte[0], 0, 0);
+
+			Assert.AreEqual(0, bytesRead);
+			stream.Verify(s => s.ReadByte(), Times.Never);
+			stream.Verify(s => s.Read(It.IsAny<byte[]>(), It.IsAny<int>(), It.IsAny<int>()), Times.Never);
+		}
+
+		[TestMethod]
+		public void MustReadByteCorrectly()
+		{
+			var sut = new SubStream(stream.Object, 100, 200);
+
+			stream.SetupGet(s => s.Position).Returns(-100);
+			Assert.AreEqual(-1, sut.ReadByte());
+
+			stream.SetupGet(s => s.Position).Returns(200);
+			Assert.AreEqual(-1, sut.ReadByte());
+
+			stream.SetupGet(s => s.Position).Returns(25);
+			sut.ReadByte();
+			stream.Verify(s => s.Read(It.IsAny<byte[]>(), It.IsAny<int>(), It.IsAny<int>()), Times.AtLeastOnce);
+		}
+
+		[TestMethod]
+		public void MustSeekCorrectly()
+		{
+			var sut = new SubStream(stream.Object, 100, 200);
+
+			sut.Seek(10, SeekOrigin.Begin);
+			Assert.AreEqual(10, sut.Position);
+
+			sut.Seek(15, SeekOrigin.Current);
+			Assert.AreEqual(25, sut.Position);
+
+			sut.Seek(-5, SeekOrigin.Current);
+			Assert.AreEqual(20, sut.Position);
+
+			sut.Seek(-50, SeekOrigin.End);
+			Assert.AreEqual(150, sut.Position);
+
+			sut.Seek(10, SeekOrigin.End);
+			Assert.AreEqual(210, sut.Position);
+
+			sut.Seek(-10, SeekOrigin.Begin);
+			Assert.AreEqual(-10, sut.Position);
+		}
+
+		[TestMethod]
+		[ExpectedException(typeof(ArgumentException))]
+		public void MustNotAllowNonReadableStream()
+		{
+			stream.SetupGet(s => s.CanRead).Returns(false);
+
+			new SubStream(stream.Object, 0, 0);
+		}
+
+		[TestMethod]
+		[ExpectedException(typeof(ArgumentException))]
+		public void MustNotAllowNonSeekableStream()
+		{
+			stream.SetupGet(s => s.CanSeek).Returns(false);
+
+			new SubStream(stream.Object, 0, 0);
+		}
+
+		[TestMethod]
+		[ExpectedException(typeof(ArgumentOutOfRangeException))]
+		public void MustNotAllowOffsetSmallerThanZero()
+		{
+			new SubStream(stream.Object, -1, 100);
+		}
+
+		[TestMethod]
+		[ExpectedException(typeof(ArgumentOutOfRangeException))]
+		public void MustNotAllowLengthSmallerThanOne()
+		{
+			new SubStream(stream.Object, 100, 0);
+		}
+
+		[TestMethod]
+		[ExpectedException(typeof(NotSupportedException))]
+		public void MustNotSupportFlushing()
+		{
+			new SubStream(stream.Object, 100, 100).Flush();
+		}
+
+		[TestMethod]
+		[ExpectedException(typeof(NotSupportedException))]
+		public void MustNotSupportChangingLength()
+		{
+			new SubStream(stream.Object, 100, 100).SetLength(100);
+		}
+
+		[TestMethod]
+		[ExpectedException(typeof(NotSupportedException))]
+		public void MustNotSupportWriting()
+		{
+			new SubStream(stream.Object, 100, 100).Write(new byte[0], 0, 0);
+		}
+	}
+}
diff --git a/SafeExamBrowser.Configuration/SubStream.cs b/SafeExamBrowser.Configuration/SubStream.cs
index 3cdda622..20e947d4 100644
--- a/SafeExamBrowser.Configuration/SubStream.cs
+++ b/SafeExamBrowser.Configuration/SubStream.cs
@@ -13,7 +13,6 @@ namespace SafeExamBrowser.Configuration
 {
 	/// <summary>
 	/// A read-only wrapper for a subsection of another, larger stream.
-	/// TODO: Unit Test!
 	/// </summary>
 	internal class SubStream : Stream
 	{