extend C++ std::string tests to cover ticket 783

tests/run/cpp_stl_string.pyx

@@ -167,6 +167,29 @@ def test_decode(char* a):
     cdef string b = string(a)
     return b.decode('ascii')
 
+
+@cython.test_assert_path_exists("//ReturnStatNode//PythonCapiCallNode")
+def test_cstr_decode(char* a):
+    """
+    >>> print(test_cstr_decode(b_asdf))
+    asdf
+    """
+    cdef string b = string(a)
+    return b.c_str().decode('utf-8')
+
+
+@cython.test_assert_path_exists("//ReturnStatNode//PythonCapiCallNode")
+@cython.test_fail_if_path_exists("//ReturnStatNode//AttributeNode")
+def test_cstr_ptr_decode(char* a):
+    """
+    >>> print(test_cstr_ptr_decode(b_asdf))
+    asdf
+    """
+    cdef string b = string(a)
+    s = b.c_str()
+    return s.decode('utf-8')
+
+
 @cython.test_assert_path_exists("//PythonCapiCallNode")
 @cython.test_fail_if_path_exists("//AttributeNode")
 def test_decode_sliced(char* a):