Added ShouldNotExist assertion to Nancy.Testing

src/Nancy.Testing.Tests/AssertExtensionsTests.cs

@@ -42,6 +42,16 @@ public void Should_not_throw_exception_when_id_does_exist()
             Assert.Null(result);
         }
 
+        [Fact]
+        public void Should_detect_nonexistence()
+        {
+            // Given, When
+            var result = Record.Exception(() => this.query["#jamesIsAwesome"].ShouldNotExist());
+
+            // Then
+            Assert.Null(result);
+        }
+
         [Fact]
         public void Should_not_throw_exception_when_id_that_should_only_exists_once_only_exists_once()
         {

src/Nancy.Testing/AssertExtensions.cs

@@ -30,6 +30,16 @@ public static AndConnector<QueryWrapper> ShouldExist(this QueryWrapper query)
             return new AndConnector<QueryWrapper>(query);
         }
 
+        /// <summary>
+        /// Asserts that an element does not exist
+        /// </summary>
+        public static AndConnector<QueryWrapper> ShouldNotExist(this QueryWrapper query)
+        {
+            Asserts.False(query.Any());
+
+            return new AndConnector<QueryWrapper>(query);
+        }
+
         /// <summary>
         /// Asserts that an element or element should exist one, and only once
         /// </summary>