[test-improver] test: add edge case tests for DoNotStoreStaticTestContextAnalyzer (#8809)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: Evangelink

test/UnitTests/MSTest.Analyzers.UnitTests/DoNotStoreStaticTestContextAnalyzerTests.cs

@@ -131,4 +131,139 @@ public static void ClassCleanup()
 
         await VerifyCS.VerifyAnalyzerAsync(code);
     }
+
+    [TestMethod]
+    public async Task WhenAssigningTestContextParameterToInstanceMember_NoDiagnostic()
+    {
+        // Assigning a TestContext *parameter* to an instance field or property should not trigger
+        // the diagnostic. This exercises the analyzer's 'Instance: null' guard while the value still
+        // satisfies the 'Value: IParameterReferenceOperation' check (only the target-side guard fails).
+        string code = """
+            using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+            [TestClass]
+            public class MyTestClass
+            {
+                private TestContext _testContext;
+                public TestContext TestContextProperty { get; set; }
+
+                public void Store(TestContext tc)
+                {
+                    _testContext = tc;
+                    TestContextProperty = tc;
+                }
+            }
+            """;
+
+        await VerifyCS.VerifyAnalyzerAsync(code);
+    }
+
+    [TestMethod]
+    public async Task WhenAssigningTestContextParameterToLocalVariable_NoDiagnostic()
+    {
+        // Assigning a TestContext parameter to a local variable is fine — the assignment target is
+        // not an IMemberReferenceOperation, so the analyzer's pattern doesn't match. An explicit
+        // assignment (not a declaration initializer) is used so OperationKind.SimpleAssignment fires.
+        string code = """
+            using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+            [TestClass]
+            public class MyTestClass
+            {
+                [AssemblyInitialize]
+                public static void AssemblyInit(TestContext tc)
+                {
+                    TestContext local;
+                    local = tc;
+                    local.WriteLine("");
+                }
+            }
+            """;
+
+        await VerifyCS.VerifyAnalyzerAsync(code);
+    }
+
+    [TestMethod]
+    public async Task WhenAssigningNonTestContextParameterToStaticField_NoDiagnostic()
+    {
+        // Covers the IParameterReferenceOperation *type-mismatch* path: the value is a parameter
+        // reference, but its type is not TestContext, so the analyzer must not fire.
+        string code = """
+            using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+            [TestClass]
+            public class MyTestClass
+            {
+                private static string s_name;
+
+                [AssemblyInitialize]
+                public static void AssemblyInit(TestContext tc)
+                {
+                    Store("value");
+                }
+
+                private static void Store(string name)
+                {
+                    s_name = name;
+                }
+            }
+            """;
+
+        await VerifyCS.VerifyAnalyzerAsync(code);
+    }
+
+    [TestMethod]
+    public async Task WhenAssigningNonParameterValueToStaticField_NoDiagnostic()
+    {
+        // Covers the 'Value is not IParameterReferenceOperation' path: a literal (or any non-parameter
+        // expression) assigned to a static field must not be flagged, even when the field type is TestContext.
+        string code = """
+            using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+            [TestClass]
+            public class MyTestClass
+            {
+                private static string s_name;
+
+                [AssemblyInitialize]
+                public static void AssemblyInit(TestContext tc)
+                {
+                    s_name = "value";
+                }
+            }
+            """;
+
+        await VerifyCS.VerifyAnalyzerAsync(code);
+    }
+
+#if NET
+    [TestMethod]
+    public async Task WhenAssigningTestContextInHelperMethod_Diagnostic()
+    {
+        // The diagnostic fires on any static member assignment of a TestContext parameter,
+        // regardless of whether the containing method is [AssemblyInitialize] or [ClassInitialize].
+        string code = """
+            using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+            [TestClass]
+            public class MyTestClass
+            {
+                private static TestContext s_testContext;
+
+                [AssemblyInitialize]
+                public static void AssemblyInit(TestContext tc)
+                {
+                    Store(tc);
+                }
+
+                private static void Store(TestContext tc)
+                {
+                    [|s_testContext = tc|];
+                }
+            }
+            """;
+
+        await VerifyCS.VerifyAnalyzerAsync(code);
+    }
+#endif
 }