diff --git a/tests/ImageProcessorCore.Tests/Helpers/GuardTests.cs b/tests/ImageProcessorCore.Tests/Helpers/GuardTests.cs
new file mode 100644
index 000000000..14b81708f
--- /dev/null
+++ b/tests/ImageProcessorCore.Tests/Helpers/GuardTests.cs
@@ -0,0 +1,204 @@
+// <copyright file="GuardTests.cs" company="James Jackson-South">
+// Copyright (c) James Jackson-South and contributors.
+// Licensed under the Apache License, Version 2.0.
+// </copyright>
+
+namespace ImageProcessorCore.Tests.Helpers
+{
+    using System;
+    using System.Diagnostics.CodeAnalysis;
+
+    using Xunit;
+
+    /// <summary>
+    /// Tests the <see cref="Guard"/> helper.
+    /// </summary>
+    public class GuardTests
+    {
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.NotNull"/> method throws when the argument is null.
+        /// </summary>
+        [Fact]
+        public void NotNullThrowsWhenArgIsNull()
+        {
+            Assert.Throws<ArgumentNullException>(() => Guard.NotNull(null, "foo"));
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.NotNull"/> method throws when the argument name is empty.
+        /// </summary>
+        [Fact]
+        public void NotNullThrowsWhenArgNameEmpty()
+        {
+            Assert.Throws<ArgumentNullException>(() => Guard.NotNull(null, string.Empty));
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.NotEmpty"/> method throws when the argument is empty.
+        /// </summary>
+        [Fact]
+        [SuppressMessage("StyleCop.CSharp.ReadabilityRules", "SA1122:UseStringEmptyForEmptyStrings", Justification = "Reviewed. Suppression is OK here.")]
+        public void NotEmptyThrowsWhenEmpty()
+        {
+            Assert.Throws<ArgumentException>(() => Guard.NotNullOrEmpty("", string.Empty));
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.NotEmpty"/> method throws when the argument is whitespace.
+        /// </summary>
+        [Fact]
+        public void NotEmptyThrowsWhenWhitespace()
+        {
+            Assert.Throws<ArgumentException>(() => Guard.NotNullOrEmpty(" ", string.Empty));
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.NotEmpty"/> method throws when the argument name is null.
+        /// </summary>
+        [Fact]
+        public void NotEmptyThrowsWhenParameterNameNull()
+        {
+            Assert.Throws<ArgumentNullException>(() => Guard.NotNullOrEmpty(null, null));
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.MustBeLessThan"/> method throws when the argument is greater.
+        /// </summary>
+        [Fact]
+        public void LessThanThrowsWhenArgIsGreater()
+        {
+            Assert.Throws<ArgumentOutOfRangeException>(() => Guard.MustBeLessThan(1, 0, "foo"));
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.MustBeLessThan"/> method throws when the argument is equal.
+        /// </summary>
+        [Fact]
+        public void LessThanThrowsWhenArgIsEqual()
+        {
+            Assert.Throws<ArgumentOutOfRangeException>(() => Guard.MustBeLessThan(1, 1, "foo"));
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.MustBeLessThanOrEqual"/> method throws when the argument is greater.
+        /// </summary>
+        [Fact]
+        public void LessThanOrEqualToThrowsWhenArgIsGreater()
+        {
+            Assert.Throws<ArgumentOutOfRangeException>(() => Guard.MustBeLessThanOrEqualTo(1, 0, "foo"));
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.MustBeLessThanOrEqual"/> method does not throw when the argument 
+        /// is less.
+        /// </summary>
+        [Fact]
+        public void LessThanOrEqualToDoesNotThrowWhenArgIsLess()
+        {
+            Exception ex = Record.Exception(() => Guard.MustBeLessThanOrEqualTo(0, 1, "foo"));
+            Assert.Null(ex);
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.MustBeLessThanOrEqual"/> method does not throw when the argument 
+        /// is equal.
+        /// </summary>
+        [Fact]
+        public void LessThanOrEqualToDoesNotThrowWhenArgIsEqual()
+        {
+            Exception ex = Record.Exception(() => Guard.MustBeLessThanOrEqualTo(1, 1, "foo"));
+            Assert.Equal(1, 1);
+            Assert.Null(ex);
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.MustBeLessThan"/> method throws when the argument is greater.
+        /// </summary>
+        [Fact]
+        public void GreaterThanThrowsWhenArgIsLess()
+        {
+            Assert.Throws<ArgumentOutOfRangeException>(() => Guard.MustBeGreaterThan(0, 1, "foo"));
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.MustBeLessThan"/> method throws when the argument is greater.
+        /// </summary>
+        [Fact]
+        public void GreaterThanThrowsWhenArgIsEqual()
+        {
+            Assert.Throws<ArgumentOutOfRangeException>(() => Guard.MustBeGreaterThan(1, 1, "foo"));
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.MustBeLessThan"/> method throws when the argument name is greater.
+        /// </summary>
+        [Fact]
+        public void GreaterThanOrEqualToThrowsWhenArgIsLess()
+        {
+            Assert.Throws<ArgumentOutOfRangeException>(() => Guard.MustBeGreaterThanOrEqualTo(0, 1, "foo"));
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.MustBeLessThanOrEqual"/> method does not throw when the argument 
+        /// is less.
+        /// </summary>
+        [Fact]
+        public void GreaterThanOrEqualToDoesNotThrowWhenArgIsGreater()
+        {
+            Exception ex = Record.Exception(() => Guard.MustBeGreaterThanOrEqualTo(1, 0, "foo"));
+            Assert.Null(ex);
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.MustBeLessThanOrEqual"/> method does not throw when the argument 
+        /// is equal.
+        /// </summary>
+        [Fact]
+        public void GreaterThanOrEqualToDoesNotThrowWhenArgIsEqual()
+        {
+            Exception ex = Record.Exception(() => Guard.MustBeGreaterThanOrEqualTo(1, 1, "foo"));
+            Assert.Equal(1, 1);
+            Assert.Null(ex);
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.MustBeBetweenOrEqualTo"/> method throws when the argument is less.
+        /// </summary>
+        [Fact]
+        public void BetweenOrEqualToThrowsWhenArgIsLess()
+        {
+            Assert.Throws<ArgumentOutOfRangeException>(() => Guard.MustBeBetweenOrEqualTo(-2, -1, 1, "foo"));
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.MustBeBetweenOrEqualTo"/> method throws when the argument is greater.
+        /// </summary>
+        [Fact]
+        public void BetweenOrEqualToThrowsWhenArgIsGreater()
+        {
+            Assert.Throws<ArgumentOutOfRangeException>(() => Guard.MustBeBetweenOrEqualTo(2, -1, 1, "foo"));
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.MustBeBetweenOrEqualTo"/> method does not throw when the argument 
+        /// is equal.
+        /// </summary>
+        [Fact]
+        public void BetweenOrEqualToDoesNotThrowWhenArgIsEqual()
+        {
+            Exception ex = Record.Exception(() => Guard.MustBeBetweenOrEqualTo(1, 1, 1, "foo"));
+            Assert.Null(ex);
+        }
+
+        /// <summary>
+        /// Tests that the <see cref="M:Guard.MustBeBetweenOrEqualTo"/> method does not throw when the argument 
+        /// is equal.
+        /// </summary>
+        [Fact]
+        public void BetweenOrEqualToDoesNotThrowWhenArgIsBetween()
+        {
+            Exception ex = Record.Exception(() => Guard.MustBeBetweenOrEqualTo(0, -1, 1, "foo"));
+            Assert.Null(ex);
+        }
+    }
+}
\ No newline at end of file
diff --git a/tests/ImageProcessorCore.Tests/Numerics/PointTests.cs b/tests/ImageProcessorCore.Tests/Numerics/PointTests.cs
new file mode 100644
index 000000000..f67e5f5b3
--- /dev/null
+++ b/tests/ImageProcessorCore.Tests/Numerics/PointTests.cs
@@ -0,0 +1,11 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+
+namespace ImageProcessor.Tests.Numerics
+{
+    public class Class
+    {
+    }
+}
diff --git a/tests/ImageProcessorCore.Tests/Numerics/RectangleTests.cs b/tests/ImageProcessorCore.Tests/Numerics/RectangleTests.cs
new file mode 100644
index 000000000..c67e9a704
--- /dev/null
+++ b/tests/ImageProcessorCore.Tests/Numerics/RectangleTests.cs
@@ -0,0 +1,66 @@
+// <copyright file="RectangleTests.cs" company="James Jackson-South">
+// Copyright (c) James Jackson-South and contributors.
+// Licensed under the Apache License, Version 2.0.
+// </copyright>
+
+namespace ImageProcessorCore.Tests
+{
+    using Xunit;
+
+    /// <summary>
+    /// Tests the <see cref="Rectangle"/> struct.
+    /// </summary>
+    public class RectangleTests
+    {
+        /// <summary>
+        /// Tests the equality operators for equality.
+        /// </summary>
+        [Fact]
+        public void AreEqual()
+        {
+            Rectangle first = new Rectangle(1, 1, 100, 100);
+            Rectangle second = new Rectangle(1, 1, 100, 100);
+
+            Assert.Equal(first, second);
+        }
+
+        /// <summary>
+        /// Tests the equality operators for inequality.
+        /// </summary>
+        [Fact]
+        public void AreNotEqual()
+        {
+            Rectangle first = new Rectangle(1, 1, 0, 100);
+            Rectangle second = new Rectangle(1, 1, 100, 100);
+
+            Assert.NotEqual(first, second);
+        }
+
+        /// <summary>
+        /// Tests whether the rectangle constructors correctly assign properties.
+        /// </summary>
+        [Fact]
+        public void ConstructorAssignsProperties()
+        {
+            Rectangle first = new Rectangle(1, 1, 50, 100);
+            Assert.Equal(1, first.X);
+            Assert.Equal(1, first.Y);
+            Assert.Equal(50, first.Width);
+            Assert.Equal(100, first.Height);
+            Assert.Equal(1, first.Top);
+            Assert.Equal(51, first.Right);
+            Assert.Equal(101, first.Bottom);
+            Assert.Equal(1, first.Left);
+
+            Rectangle second = new Rectangle(new Point(1, 1), new Size(50, 100));
+            Assert.Equal(1, second.X);
+            Assert.Equal(1, second.Y);
+            Assert.Equal(50, second.Width);
+            Assert.Equal(100, second.Height);
+            Assert.Equal(1, second.Top);
+            Assert.Equal(51, second.Right);
+            Assert.Equal(101, second.Bottom);
+            Assert.Equal(1, second.Left);
+        }
+    }
+}
\ No newline at end of file
diff --git a/tests/ImageProcessorCore.Tests/Numerics/SizeTests.cs b/tests/ImageProcessorCore.Tests/Numerics/SizeTests.cs
new file mode 100644
index 000000000..56b2ffa20
--- /dev/null
+++ b/tests/ImageProcessorCore.Tests/Numerics/SizeTests.cs
@@ -0,0 +1,50 @@
+// <copyright file="SizeTests.cs" company="James Jackson-South">
+// Copyright (c) James Jackson-South and contributors.
+// Licensed under the Apache License, Version 2.0.
+// </copyright>
+
+namespace ImageProcessorCore.Tests
+{
+    using Xunit;
+
+    /// <summary>
+    /// Tests the <see cref="Size"/> struct.
+    /// </summary>
+    public class SizeTests
+    {
+        /// <summary>
+        /// Tests the equality operators for equality.
+        /// </summary>
+        [Fact]
+        public void AreEqual()
+        {
+            Size first = new Size(100, 100);
+            Size second = new Size(100, 100);
+
+            Assert.Equal(first, second);
+        }
+
+        /// <summary>
+        /// Tests the equality operators for inequality.
+        /// </summary>
+        [Fact]
+        public void AreNotEqual()
+        {
+            Size first = new Size(0, 100);
+            Size second = new Size(100, 100);
+
+            Assert.NotEqual(first, second);
+        }
+
+        /// <summary>
+        /// Tests whether the size constructor correctly assign properties.
+        /// </summary>
+        [Fact]
+        public void ConstructorAssignsProperties()
+        {
+            Size first = new Size(4, 5);
+            Assert.Equal(4, first.Width);
+            Assert.Equal(5, first.Height);
+        }
+    }
+}
\ No newline at end of file