S1871 Add reported FP to test cases.

java-checks-test-sources/default/src/main/java/checks/IdenticalCasesInSwitchCheckSample.java

@@ -216,4 +216,36 @@ private void f() {
   private void f(int i) {
   }
 
+  static class Parent {};
+  static class A extends Parent {};
+  static class B extends Parent {};
+
+  // Edge case FP.
+  // See: https://community.sonarsource.com/t/fp-java-s1871-branch-code-block-is-the-same/130645
+  void variablesBoundInInstanceOf() {
+    Parent p1 = new A();
+    Parent p2 = new B();
+    if(Math.random() < 0.5) {
+      p1 = new B();
+      p2 = new A();
+    }
+
+    Parent p = null;
+    if (p1 instanceof A a) {
+//                         ^[el=+3;ec=5]> 1 {{Original}}
+      p = a;
+    }
+    else if (p2 instanceof A a) { // Noncompliant {{This branch's code block is the same as the block for the branch on line 234.}}
+//                              ^[el=+3;ec=5]
+      p = a;
+    }
+
+    // Renaming variables fixes the issue.
+    if (p1 instanceof A a1) {
+      p = a1;
+    }
+    else if (p2 instanceof A a2) {
+      p = a2;
+    }
+  }
 }