Adding template class specialization sequence diagram test case

tests/t20006/t20006.cc

@@ -0,0 +1,30 @@
+#include <string>
+
+namespace clanguml {
+namespace t20006 {
+
+template <typename T> struct A {
+    T a(T arg) { return arg; }
+    T a1(T arg) { return arg; }
+};
+
+template <typename T> struct B {
+    T b(T arg) { return a_.a(arg); }
+    A<T> a_;
+};
+
+template <> struct B<std::string> {
+    std::string b(std::string arg) { return arg; }
+    A<std::string> a_;
+};
+
+void tmain()
+{
+    B<int> bint;
+    B<std::string> bstring;
+
+    bint.b(1);
+    bstring.b("bstring");
+}
+}
+}