Add assertions on JSON nodes null, string, number, true, and false.

Src/FluentAssertions/Json/JsonElementAssertions.cs

@@ -42,6 +42,108 @@ public AndConstraint<JsonElementAssertions> HaveValueKind(JsonValueKind valueKin
         return new(this);
     }
 
+    /// <summary>
+    ///     Asserts that the current <see cref="JsonElement"/> is the JSON null node.
+    /// </summary>
+    /// <param name="because">
+    ///     A formatted phrase as is supported by <see cref="string.Format(string,object[])" /> explaining why the assertion
+    ///     is needed. If the phrase does not start with the word <i>because</i>, it is prepended automatically.
+    /// </param>
+    /// <param name="becauseArgs">
+    ///     Zero or more objects to format using the placeholders in <see paramref="because" />.
+    /// </param>
+    public AndConstraint<JsonElementAssertions> BeNull(string because = "", params object[] becauseArgs)
+    {
+        Execute.Assertion
+            .BecauseOf(because, becauseArgs)
+            .ForCondition(Subject.ValueKind == JsonValueKind.Null)
+            .FailWith("Expected {context:JSON} to be a JSON null{reason}, but found {0}.", Subject);
+
+        return new(this);
+    }
+
+    /// <summary>
+    ///     Asserts that the current <see cref="JsonElement"/> is the JSON string node.
+    /// </summary>
+    /// <param name="value">The value of the JSON string node.</param>
+    /// <param name="because">
+    ///     A formatted phrase as is supported by <see cref="string.Format(string,object[])" /> explaining why the assertion
+    ///     is needed. If the phrase does not start with the word <i>because</i>, it is prepended automatically.
+    /// </param>
+    /// <param name="becauseArgs">
+    ///     Zero or more objects to format using the placeholders in <see paramref="because" />.
+    /// </param>
+    public AndConstraint<JsonElementAssertions> BeString(string value, string because = "", params object[] becauseArgs)
+    {
+        Execute.Assertion
+            .BecauseOf(because, becauseArgs)
+            .ForCondition(Subject.ValueKind == JsonValueKind.String && Subject.GetString() == value)
+            .FailWith("Expected {context:JSON} to be a JSON string {0}{reason}, but found {1}.", value, Subject);
+
+        return new(this);
+    }
+
+    /// <summary>
+    ///     Asserts that the current <see cref="JsonElement"/> is the JSON number node.
+    /// </summary>
+    /// <param name="value">The value of the JSON string node.</param>
+    /// <param name="because">
+    ///     A formatted phrase as is supported by <see cref="string.Format(string,object[])" /> explaining why the assertion
+    ///     is needed. If the phrase does not start with the word <i>because</i>, it is prepended automatically.
+    /// </param>
+    /// <param name="becauseArgs">
+    ///     Zero or more objects to format using the placeholders in <see paramref="because" />.
+    /// </param>
+    public AndConstraint<JsonElementAssertions> BeNumber(decimal value, string because = "", params object[] becauseArgs)
+    {
+        Execute.Assertion
+            .BecauseOf(because, becauseArgs)
+            .ForCondition(Subject.ValueKind == JsonValueKind.Number && Subject.GetDecimal() == value)
+            .FailWith("Expected {context:JSON} to be a JSON string {0}{reason}, but found {1}.", value, Subject);
+
+        return new(this);
+    }
+
+    /// <summary>
+    ///     Asserts that the current <see cref="JsonElement"/> is the JSON true node.
+    /// </summary>
+    /// <param name="because">
+    ///     A formatted phrase as is supported by <see cref="string.Format(string,object[])" /> explaining why the assertion
+    ///     is needed. If the phrase does not start with the word <i>because</i>, it is prepended automatically.
+    /// </param>
+    /// <param name="becauseArgs">
+    ///     Zero or more objects to format using the placeholders in <see paramref="because" />.
+    /// </param>
+    public AndConstraint<JsonElementAssertions> BeTrue(string because = "", params object[] becauseArgs)
+    {
+        Execute.Assertion
+            .BecauseOf(because, becauseArgs)
+            .ForCondition(Subject.ValueKind == JsonValueKind.True)
+            .FailWith("Expected {context:JSON} to be a JSON true{reason}, but found {0}.", Subject);
+
+        return new(this);
+    }
+
+    /// <summary>
+    ///     Asserts that the current <see cref="JsonElement"/> is the JSON false node.
+    /// </summary>
+    /// <param name="because">
+    ///     A formatted phrase as is supported by <see cref="string.Format(string,object[])" /> explaining why the assertion
+    ///     is needed. If the phrase does not start with the word <i>because</i>, it is prepended automatically.
+    /// </param>
+    /// <param name="becauseArgs">
+    ///     Zero or more objects to format using the placeholders in <see paramref="because" />.
+    /// </param>
+    public AndConstraint<JsonElementAssertions> BeFalse(string because = "", params object[] becauseArgs)
+    {
+        Execute.Assertion
+            .BecauseOf(because, becauseArgs)
+            .ForCondition(Subject.ValueKind == JsonValueKind.False)
+            .FailWith("Expected {context:JSON} to be JSON false{reason}, but found {0}.", Subject);
+
+        return new(this);
+    }
+
     public void Be(long jsonNumber)
     {
         Execute.Assertion

Tests/FluentAssertions.Specs/Json/JsonElementAssertionsSpecs.cs

@@ -17,11 +17,11 @@ public void Throws_for_unexcepected_value_kind()
 
             // Act
             Action act = () => options.Should().Serialize(42)
-                .And.Value.Should().HaveValueKind(JsonValueKind.String, because: "Why not?");
+                .And.Value.Should().HaveValueKind(JsonValueKind.String, because: "why not?");
 
             // Assert
             act.Should().Throw<XunitException>()
-                .WithMessage("Expected options to have value kind JsonValueKind.String {value: 3} because Why not?, but found JsonValueKind.Number {value: 4}");
+                .WithMessage("Expected options to have value kind JsonValueKind.String {value: 3} because why not?, but found JsonValueKind.Number {value: 4}.");
         }
 
         [Fact]
@@ -34,4 +34,149 @@ public void Guards_excepected_value_kinds()
             options.Should().Serialize(42).And.Value.Should().HaveValueKind(JsonValueKind.Number);
         }
     }
+
+    public class BeNull
+    {
+        [Fact]
+        public void Throws_for_other_elements()
+        {
+            // Arrange
+            JsonSerializerOptions options = new();
+
+            // Act
+            Action act = () => options.Should().Serialize("null").And.Value.Should().BeNull(because: "why not?");
+
+            // Assert
+            act.Should().Throw<XunitException>()
+                .WithMessage("TODO");
+        }
+
+        [Fact]
+        public void Guards_null_node()
+        {
+            // Arrange
+            JsonSerializerOptions options = new();
+
+            // Act + assert
+            options.Should().Serialize<object>(null).And.Value.Should().BeNull();
+        }
+    }
+
+    public class BeString
+    {
+        [Fact]
+        public void Throws_for_other_elements()
+        {
+            // Arrange
+            JsonSerializerOptions options = new();
+
+            // Act
+            Action act = () => options.Should().Serialize<object>(null).And.Value.Should().BeString("null", because: "why not?");
+
+            // Assert
+            act.Should().Throw<XunitException>()
+                .WithMessage("TODO");
+        }
+
+        [Fact]
+        public void Guards_string_node()
+        {
+            // Arrange
+            JsonSerializerOptions options = new();
+
+            // Act + assert
+            options.Should().Serialize(Guid.Parse("61088fce-43c5-4327-b591-0d7e862075d8")).And.Value.Should().BeString("61088fce-43c5-4327-b591-0d7e862075d8");
+        }
+    }
+
+    public class BeNumber
+    {
+        [Fact]
+        public void Throws_for_other_elements()
+        {
+            // Arrange
+            JsonSerializerOptions options = new();
+
+            // Act
+            Action act = () => options.Should().Serialize("42").And.Value.Should().BeNumber(42, because: "why not?");
+
+            // Assert
+            act.Should().Throw<XunitException>()
+                .WithMessage("TODO");
+        }
+
+        [Fact]
+        public void Guards_integer_number_node()
+        {
+            // Arrange
+            JsonSerializerOptions options = new();
+
+            // Act + assert
+            options.Should().Serialize(42).And.Value.Should().BeNumber(42);
+        }
+
+        [Fact]
+        public void Guards_floating_point_number_node()
+        {
+            // Arrange
+            JsonSerializerOptions options = new();
+
+            // Act + assert
+            options.Should().Serialize(42.17).And.Value.Should().BeNumber(42.17m);
+        }
+    }
+
+    public class BeTrue
+    {
+        [Fact]
+        public void Throws_for_other_elements()
+        {
+            // Arrange
+            JsonSerializerOptions options = new();
+
+            // Act
+            Action act = () => options.Should().Serialize("true").And.Value.Should().BeTrue(because: "why not?");
+
+            // Assert
+            act.Should().Throw<XunitException>()
+                .WithMessage("TODO");
+        }
+
+        [Fact]
+        public void Guards_true_node()
+        {
+            // Arrange
+            JsonSerializerOptions options = new();
+
+            // Act + assert
+            options.Should().Serialize(true).And.Value.Should().BeTrue();
+        }
+    }
+
+    public class BeFalse
+    {
+        [Fact]
+        public void Throws_for_other_elements()
+        {
+            // Arrange
+            JsonSerializerOptions options = new();
+
+            // Act
+            Action act = () => options.Should().Serialize("false").And.Value.Should().BeFalse(because: "why not?");
+
+            // Assert
+            act.Should().Throw<XunitException>()
+                .WithMessage("TODO");
+        }
+
+        [Fact]
+        public void Guards_false_node()
+        {
+            // Arrange
+            JsonSerializerOptions options = new();
+
+            // Act + assert
+            options.Should().Serialize(false).And.Value.Should().BeFalse();
+        }
+    }
 }