feat: add missing nunit test cases for null assertions (#338)

Author: Meir017

docs/NunitAnalyzer.md

@@ -105,6 +105,7 @@ object obj = null;
 // old assertion:
 Assert.IsNull(obj);
 Assert.Null(obj);
+Assert.That(obj, Is.Null);
 
 // new assertion:
 obj.Should().BeNull();
@@ -122,6 +123,9 @@ Assert.Null(obj); /* fail message:   Expected: null
 Assert.IsNull(obj); /* fail message:   Expected: null
   But was:  "foo"
  */
+Assert.That(obj, Is.Null); /* fail message:   Expected: null
+  But was:  "foo"
+ */
 
 // new assertion:
 obj.Should().BeNull(); /* fail message: Expected obj to be <null>, but found "foo". */
@@ -136,6 +140,7 @@ object obj = "foo";
 // old assertion:
 Assert.IsNotNull(obj);
 Assert.NotNull(obj);
+Assert.That(obj, Is.Not.Null);
 
 // new assertion:
 obj.Should().NotBeNull();
@@ -153,6 +158,9 @@ Assert.NotNull(obj); /* fail message:   Expected: not null
 Assert.IsNotNull(obj); /* fail message:   Expected: not null
   But was:  null
  */
+Assert.That(obj, Is.Not.Null); /* fail message:   Expected: not null
+  But was:  null
+ */
 
 // new assertion:
 obj.Should().NotBeNull(); /* fail message: Expected obj not to be <null>. */

src/FluentAssertions.Analyzers.FluentAssertionAnalyzerDocs/NunitAnalyzerTests.cs

@@ -161,6 +161,7 @@ public void AssertNull()
         // old assertion:
         Assert.IsNull(obj);
         Assert.Null(obj);
+        Assert.That(obj, Is.Null);
 
         // new assertion:
         obj.Should().BeNull();
@@ -186,6 +187,16 @@ public void AssertNull_Failure_OldAssertion_1()
         Assert.IsNull(obj);
     }
 
+    [TestMethod, ExpectedTestFrameworkException]
+    public void AssertNull_Failure_OldAssertion_2()
+    {
+        // arrange
+        object obj = "foo";
+
+        // old assertion:
+        Assert.That(obj, Is.Null);
+    }
+
     [TestMethod, ExpectedTestFrameworkException]
     public void AssertNull_Failure_NewAssertion()
     {
@@ -205,6 +216,7 @@ public void AssertNotNull()
         // old assertion:
         Assert.IsNotNull(obj);
         Assert.NotNull(obj);
+        Assert.That(obj, Is.Not.Null);
 
         // new assertion:
         obj.Should().NotBeNull();
@@ -230,6 +242,16 @@ public void AssertNotNull_Failure_OldAssertion_1()
         Assert.IsNotNull(obj);
     }
 
+    [TestMethod, ExpectedTestFrameworkException]
+    public void AssertNotNull_Failure_OldAssertion_2()
+    {
+        // arrange
+        object obj = null;
+
+        // old assertion:
+        Assert.That(obj, Is.Not.Null);
+    }
+
     [TestMethod, ExpectedTestFrameworkException]
     public void AssertNotNull_Failure_NewAssertion()
     {

src/FluentAssertions.Analyzers.Tests/Tips/NunitTests.cs

@@ -153,6 +153,7 @@ public class NunitTests
     [DataTestMethod]
     [AssertionDiagnostic("Assert.Null(actual{0});")]
     [AssertionDiagnostic("Assert.IsNull(actual{0});")]
+    [AssertionDiagnostic("Assert.That(actual, Is.Null{0});")]
     [Implemented]
     public void Nunit3_AssertNull_TestAnalyzer(string assertion) => Nunit3VerifyDiagnostic("object actual", assertion);
 
@@ -169,6 +170,9 @@ public class NunitTests
     [AssertionCodeFix(
         oldAssertion: "Assert.IsNull(actual{0});",
         newAssertion: "actual.Should().BeNull({0});")]
+    [AssertionCodeFix(
+        oldAssertion: "Assert.That(actual, Is.Null{0});",
+        newAssertion: "actual.Should().BeNull({0});")]
     [Implemented]
     public void Nunit3_AssertNull_TestCodeFix(string oldAssertion, string newAssertion) => Nunit3VerifyFix("object actual", oldAssertion, newAssertion);
 
@@ -185,6 +189,7 @@ public class NunitTests
     [DataTestMethod]
     [AssertionDiagnostic("Assert.NotNull(actual{0});")]
     [AssertionDiagnostic("Assert.IsNotNull(actual{0});")]
+    [AssertionDiagnostic("Assert.That(actual, Is.Not.Null{0});")]
     [Implemented]
     public void Nunit3_AssertNotNull_TestAnalyzer(string assertion) => Nunit3VerifyDiagnostic("object actual", assertion);
 
@@ -201,6 +206,9 @@ public class NunitTests
     [AssertionCodeFix(
         oldAssertion: "Assert.IsNotNull(actual{0});",
         newAssertion: "actual.Should().NotBeNull({0});")]
+    [AssertionCodeFix(
+        oldAssertion: "Assert.That(actual, Is.Not.Null{0});",
+        newAssertion: "actual.Should().NotBeNull({0});")]
     [Implemented]
     public void Nunit3_AssertNotNull_TestCodeFix(string oldAssertion, string newAssertion) => Nunit3VerifyFix("object actual", oldAssertion, newAssertion);
 

src/FluentAssertions.Analyzers/Tips/NunitCodeFixProvider.cs

@@ -249,6 +249,10 @@ private CreateChangedDocument TryComputeFixForNunitThat(IInvocationOperation inv
             case "True" when constraint.Instance is IPropertyReferenceOperation { Property.Name: "Not" } chainedReference && PropertyReferencedFromType(chainedReference, t.Is): // Assert.That(subject, Is.Not.True)
             case "False" when PropertyReferencedFromType(constraint, t.Is): // Assert.That(subject, Is.False)
                 return DocumentEditorUtils.RenameMethodToSubjectShouldAssertion(invocation, context, "BeFalse", subjectIndex: 0, argumentsToRemove: [1]);
+            case "Null" when PropertyReferencedFromType(constraint, t.Is): // Assert.That(subject, Is.Null)
+                return DocumentEditorUtils.RenameMethodToSubjectShouldAssertion(invocation, context, "BeNull", subjectIndex: 0, argumentsToRemove: [1]);
+            case "Null" when constraint.Instance is IPropertyReferenceOperation { Property.Name: "Not" } chainedReference && PropertyReferencedFromType(chainedReference, t.Is): // Assert.That(subject, Is.Not.Null)
+                return DocumentEditorUtils.RenameMethodToSubjectShouldAssertion(invocation, context, "NotBeNull", subjectIndex: 0, argumentsToRemove: [1]);
 
             default:
                 return null;