Added guards and unit tests for the Bootstrapper.

src/ImageSharp/Bootstrapper.cs

@@ -64,9 +64,41 @@ namespace ImageSharp
         /// <param name="format">The new format to add.</param>
         public void AddImageFormat(IImageFormat format)
         {
-            if (this.imageFormats.All(i => i.GetType() != format.GetType()))
+            Guard.NotNull(format, nameof(format));
+            Guard.NotNull(format.Encoder, nameof(format), "The encoder should not be null.");
+            Guard.NotNull(format.Decoder, nameof(format), "The decoder should not be null.");
+            Guard.NotNullOrEmpty(format.MimeType, nameof(format), "The mime type should not be null or empty.");
+            Guard.NotNullOrEmpty(format.Extension, nameof(format), "The extension should not be null or empty.");
+            Guard.NotNullOrEmpty(format.SupportedExtensions, nameof(format), "The supported extensions not be null or empty.");
+
+            GuardDuplicate(format);
+
+            this.imageFormats.Add(format);
+        }
+
+        private void GuardDuplicate(IImageFormat format)
+        {
+            if (!format.SupportedExtensions.Contains(format.Extension, StringComparer.OrdinalIgnoreCase))
+            {
+                throw new ArgumentException("The supported extensions should contain the default extension.", nameof(format));
+            }
+
+            if (format.SupportedExtensions.Any(e => string.IsNullOrWhiteSpace(e)))
+            {
+                throw new ArgumentException("The supported extensions should not contain empty values.", nameof(format));
+            }
+
+            foreach (var imageFormat in this.imageFormats)
             {
-                this.imageFormats.Add(format);
+                if (imageFormat.Extension.Equals(format.Extension, StringComparison.OrdinalIgnoreCase))
+                {
+                    throw new ArgumentException("There is already a format with the same extension.", nameof(format));
+                }
+
+                if (imageFormat.SupportedExtensions.Intersect(format.SupportedExtensions, StringComparer.OrdinalIgnoreCase).Any())
+                {
+                    throw new ArgumentException("There is already a format that supports the same extension.", nameof(format));
+                }
             }
         }
     }

src/ImageSharp/Common/Helpers/Guard.cs

@@ -6,7 +6,9 @@
 namespace ImageSharp
 {
     using System;
+    using System.Collections.Generic;
     using System.Diagnostics;
+    using System.Linq;
 
     /// <summary>
     /// Provides methods to protect against invalid parameters.
@@ -42,21 +44,47 @@ namespace ImageSharp
         /// </summary>
         /// <param name="target">The target string, which should be checked against being null or empty.</param>
         /// <param name="parameterName">Name of the parameter.</param>
+        /// <param name="message">The error message, if any to add to the exception.</param>
         /// <exception cref="ArgumentNullException"><paramref name="target"/> is null.</exception>
         /// <exception cref="ArgumentException"><paramref name="target"/> is empty or contains only blanks.</exception>
-        public static void NotNullOrEmpty(string target, string parameterName)
+        public static void NotNullOrEmpty(string target, string parameterName, string message = "")
         {
-            if (target == null)
-            {
-                throw new ArgumentNullException(parameterName);
-            }
+            NotNull(target, parameterName, message);
 
             if (string.IsNullOrWhiteSpace(target))
             {
+                if (!string.IsNullOrWhiteSpace(message))
+                {
+                    throw new ArgumentException(message, parameterName);
+                }
+
                 throw new ArgumentException("Value cannot be null or empty and cannot contain only blanks.", parameterName);
             }
         }
 
+        /// <summary>
+        /// Verifies, that the enumeration is not null and not empty.
+        /// </summary>
+        /// <param name="target">The target enumeration, which should be checked against being null or empty.</param>
+        /// <param name="parameterName">Name of the parameter.</param>
+        /// <param name="message">The error message, if any to add to the exception.</param>
+        /// <exception cref="ArgumentNullException"><paramref name="target"/> is null.</exception>
+        /// <exception cref="ArgumentException"><paramref name="target"/> is empty.</exception>
+        public static void NotNullOrEmpty<T>(IEnumerable<T> target, string parameterName, string message = "")
+        {
+            NotNull(target, parameterName, message);
+
+            if (!target.Any())
+            {
+                if (!string.IsNullOrWhiteSpace(message))
+                {
+                    throw new ArgumentException(message, parameterName);
+                }
+
+                throw new ArgumentException("Value cannot be empty.", parameterName);
+            }
+        }
+
         /// <summary>
         /// Verifies that the specified value is less than a maximum value
         /// and throws an exception if it is not.

tests/ImageSharp.Tests/BootstrapperTests.cs

@@ -0,0 +1,160 @@
+// <copyright file="BootstrapperTests.cs" company="James Jackson-South">
+// Copyright (c) James Jackson-South and contributors.
+// Licensed under the Apache License, Version 2.0.
+// </copyright>
+
+namespace ImageSharp.Tests
+{
+    using System;
+    using System.Collections.Generic;
+    using ImageSharp.Formats;
+    using Xunit;
+    using System.Linq;
+
+    public class BootstrapperTests
+    {
+        private class TestFormat : IImageFormat
+        {
+            private IImageDecoder decoder;
+            private IImageEncoder encoder;
+            private string mimeType;
+            private string extension;
+            private IEnumerable<string> supportedExtensions;
+
+            public TestFormat()
+            {
+                this.decoder = new JpegDecoder();
+                this.encoder = new JpegEncoder();
+                this.extension = "jpg";
+                this.mimeType = "image/test";
+                this.supportedExtensions = new string[] { "jpg" };
+            }
+
+            public IImageDecoder Decoder { get { return this.decoder; } set { this.decoder = value; } }
+
+            public IImageEncoder Encoder { get { return this.encoder; } set { this.encoder = value; } }
+
+            public string MimeType { get { return this.mimeType; } set { this.mimeType = value; } }
+
+            public string Extension { get { return this.extension; } set { this.extension = value; } }
+
+            public IEnumerable<string> SupportedExtensions { get { return this.supportedExtensions; } set { this.supportedExtensions = value; } }
+        }
+
+        [Fact]
+        public void AddImageFormatGuardNull()
+        {
+            ArgumentException exception;
+
+            exception = Assert.Throws<ArgumentNullException>(() =>
+            {
+                Bootstrapper.Instance.AddImageFormat(null);
+            });
+
+            var format = new TestFormat();
+            format.Decoder = null;
+
+            exception = Assert.Throws<ArgumentNullException>(() =>
+            {
+                Bootstrapper.Instance.AddImageFormat(format);
+            });
+            Assert.Contains("decoder", exception.Message);
+
+            format = new TestFormat();
+            format.Encoder = null;
+
+            exception = Assert.Throws<ArgumentNullException>(() =>
+            {
+                Bootstrapper.Instance.AddImageFormat(format);
+            });
+            Assert.Contains("encoder", exception.Message);
+
+            format = new TestFormat();
+            format.MimeType = null;
+
+            exception = Assert.Throws<ArgumentNullException>(() =>
+            {
+                Bootstrapper.Instance.AddImageFormat(format);
+            });
+            Assert.Contains("mime type", exception.Message);
+
+            format = new TestFormat();
+            format.MimeType = "";
+
+            exception = Assert.Throws<ArgumentException>(() =>
+            {
+                Bootstrapper.Instance.AddImageFormat(format);
+            });
+            Assert.Contains("mime type", exception.Message);
+
+            format = new TestFormat();
+            format.Extension = null;
+
+            exception = Assert.Throws<ArgumentNullException>(() =>
+            {
+                Bootstrapper.Instance.AddImageFormat(format);
+            });
+            Assert.Contains("extension", exception.Message);
+
+            format = new TestFormat();
+            format.Extension = "";
+
+            exception = Assert.Throws<ArgumentException>(() =>
+            {
+                Bootstrapper.Instance.AddImageFormat(format);
+            });
+            Assert.Contains("extension", exception.Message);
+
+            format = new TestFormat();
+            format.SupportedExtensions = null;
+
+            exception = Assert.Throws<ArgumentNullException>(() =>
+            {
+                Bootstrapper.Instance.AddImageFormat(format);
+            });
+            Assert.Contains("supported extensions", exception.Message);
+
+            format = new TestFormat();
+            format.SupportedExtensions = Enumerable.Empty<string>();
+
+            exception = Assert.Throws<ArgumentException>(() =>
+            {
+                Bootstrapper.Instance.AddImageFormat(format);
+            });
+            Assert.Contains("supported extensions", exception.Message);
+        }
+
+        [Fact]
+        public void AddImageFormatChecks()
+        {
+            var format = new TestFormat();
+
+            var exception = Assert.Throws<ArgumentException>(() =>
+            {
+                Bootstrapper.Instance.AddImageFormat(format);
+            });
+            Assert.Contains("format with the same", exception.Message);
+
+            format.Extension = "test";
+            exception = Assert.Throws<ArgumentException>(() =>
+            {
+                Bootstrapper.Instance.AddImageFormat(format);
+            });
+            Assert.Contains("should contain", exception.Message);
+
+            format.SupportedExtensions = new string[] { "test", "jpg" };
+            exception = Assert.Throws<ArgumentException>(() =>
+            {
+                Bootstrapper.Instance.AddImageFormat(format);
+            });
+            Assert.Contains("supports the same", exception.Message);
+
+            format.SupportedExtensions = new string[] { "test", "" };
+            exception = Assert.Throws<ArgumentException>(() =>
+            {
+                Bootstrapper.Instance.AddImageFormat(format);
+            });
+            Assert.Contains("empty values", exception.Message);
+        }
+    }
+}