Add test for ObjFlow over binding patterns

java/ql/test/library-tests/object-tostring-flow-binding-patterns/Test.java

@@ -0,0 +1,29 @@
+public class Test {
+
+  interface Intf { }
+  static class Specific implements Intf { public String toString() { return "Specific"; } }
+  static class Alternative implements Intf { public String toString() { return "Alternative"; } }
+
+  public static String caller() {
+
+    Alternative a = new Alternative(); // Instantiate this somewhere so there are at least two candidate types in general
+    return test(new Specific());
+
+  }
+
+  public static String test(Object o) {
+
+    if (o instanceof Object o2) {
+      // So we should know o2.toString is really Specific.toString():
+      return o2.toString();
+    }
+
+    switch (o) {
+      case Object o2 when o2.hashCode() > 0 -> { return o2.toString(); } // Same goes for this `o2`
+      default -> { return "Not an Intf"; }
+    }
+
+  }
+
+}
+