Added uuid format for schema validation (#1325)

- Created new uuid format validator
- Added testing for format

src/NJsonSchema.Tests/Validation/FormatUuidTests.cs

@@ -0,0 +1,46 @@
+using System;
+using System.Linq;
+using Newtonsoft.Json.Linq;
+using NJsonSchema.Validation;
+using Xunit;
+
+namespace NJsonSchema.Tests.Validation
+{
+    public class FormatUuidTests
+    {
+        [Fact]
+        public void When_format_uuid_incorrect_then_validation_succeeds()
+        {
+            //// Arrange
+            var schema = new JsonSchema();
+            schema.Type = JsonObjectType.String;
+            schema.Format = JsonFormatStrings.Uuid;
+
+            var token = new JValue("test");
+
+            //// Act
+            var errors = schema.Validate(token);
+
+            //// Assert
+            Assert.Equal(ValidationErrorKind.UuidExpected, errors.First().Kind);
+        }
+
+        [Fact]
+        public void When_format_uuid_correct_then_validation_succeeds()
+        {
+            //// Arrange
+            var schema = new JsonSchema();
+            schema.Type = JsonObjectType.String;
+            schema.Format = JsonFormatStrings.Uuid;
+
+            var uuid = Guid.NewGuid().ToString(); 
+            var token = new JValue(uuid);
+
+            //// Act
+            var errors = schema.Validate(token);
+
+            //// Assert
+            Assert.Empty(errors);
+        }
+    }
+}

src/NJsonSchema/Validation/FormatValidators/UuidFormatValidator.cs

@@ -0,0 +1,34 @@
+//-----------------------------------------------------------------------
+// <copyright file="UuidFormatValidator.cs" company="NJsonSchema">
+//     Copyright (c) Rico Suter. All rights reserved.
+// </copyright>
+// <license>https://github.com/RicoSuter/NJsonSchema/blob/master/LICENSE.md</license>
+// <author>Rico Suter, mail@rsuter.com</author>
+//-----------------------------------------------------------------------
+
+using Newtonsoft.Json.Linq;
+using System;
+
+namespace NJsonSchema.Validation.FormatValidators
+{
+    /// <summary>Validator for "Uuid" format.</summary>
+    public class UuidFormatValidator : IFormatValidator
+    {
+        /// <summary>Gets the format attribute's value.</summary>
+        #pragma warning disable CS0618 // Type or member is obsolete
+        public string Format { get; } = JsonFormatStrings.Uuid;
+        #pragma warning restore CS0618 // Type or member is obsolete
+
+        /// <summary>Gets the kind of error produced by validator.</summary>
+        public ValidationErrorKind ValidationErrorKind { get; } = ValidationErrorKind.UuidExpected;
+
+        /// <summary>Validates format of given value.</summary>
+        /// <param name="value">String value.</param>
+        /// <param name="tokenType">Type of token holding the value.</param>
+        /// <returns>True if value is correct for given format, False - if not.</returns>
+        public bool IsValid(string value, JTokenType tokenType)
+        {
+            return Guid.TryParse(value, out Guid guid);
+        }
+    }
+}

src/NJsonSchema/Validation/JsonSchemaValidator.cs

@@ -33,7 +33,8 @@ public class JsonSchemaValidator
             new TimeSpanFormatValidator(),
             new UriFormatValidator(),
             new ByteFormatValidator(),
-            new Base64FormatValidator()
+            new Base64FormatValidator(),
+            new UuidFormatValidator()
         };
 
         private readonly IDictionary<string, IFormatValidator[]> _formatValidatorsMap;

src/NJsonSchema/Validation/ValidationErrorKind.cs

@@ -141,6 +141,9 @@ public enum ValidationErrorKind
         Base64Expected,
 
         /// <summary>No type of the types does validate (check error details in <see cref="MultiTypeValidationError"/>). </summary>
-        NoTypeValidates
+        NoTypeValidates,
+
+        /// <summary>A valid UUID is expected. </summary>
+        UuidExpected,
     }
 }