Add testcase for using declaration and extend for flattening class

Closes #1581

Examples/test-suite/common.mk

@@ -586,6 +586,7 @@ CPP_TEST_CASES += \
 	using_directive_and_declaration \
 	using_directive_and_declaration_forward \
 	using_extend \
+	using_extend_flatten \
 	using_inherit \
 	using_member \
 	using_member_multiple_inherit \

Examples/test-suite/java/using_extend_flatten_runme.java

@@ -0,0 +1,21 @@
+
+import using_extend_flatten.*;
+
+public class using_extend_flatten_runme {
+
+  static {
+    try {
+	System.loadLibrary("using_extend_flatten");
+    } catch (UnsatisfiedLinkError e) {
+      System.err.println("Native code library failed to load. See the chapter on Dynamic Linking Problems in the SWIG Java documentation for help.\n" + e);
+      System.exit(1);
+    }
+  }
+
+  public static void main(String argv[]) {
+    ExtendDerived ed = new ExtendDerived();
+    ed.one();
+    ed.two();
+    ed.three();
+  }
+}

Examples/test-suite/using_extend_flatten.i

@@ -0,0 +1,34 @@
+%module using_extend_flatten
+
+// Issue #1581 - how to flatten all the methods in a base class into a derived class.
+// Just ExtendDerived is exposed including the methods from the base class, exposed via a using declaration.
+
+%extend ExtendDerived {
+    using ExtendBase::one;
+}
+%ignore ExtendBase;
+
+%inline %{
+class ExtendBase
+{
+public:
+    void one();
+    virtual void two();
+    virtual void three();
+};
+
+class ExtendDerived : public ExtendBase
+{
+public:
+    void two() override;
+    void three() override;
+};
+%}
+
+%{
+void ExtendBase::one() {}
+void ExtendBase::two() {}
+void ExtendBase::three() {}
+void ExtendDerived::two() {}
+void ExtendDerived::three() {}
+%}