Update the contents

sphinx/interface.rst

@@ -4,9 +4,19 @@ Programming interface
 Assertions
 ----------
 
+The functions described in this section is declared in the `cppunitx::assertion`
+namespace.
+
 .. cpp:namespace:: cppunitx::assertion
 
+.. cpp:function:: template<class T, class U> \
+                  void assertEqual(T x, U y, const char *message = nullptr)
+                  template<class T, class U> \
+                  void assertEqual(T x, U y, const std::string &message)
+
+   This function asserts two values are equal to each other.
+
 .. cpp:function:: void fail(const char *message = nullptr)
                   void fail(const std::string &message)
 
-   This function throws an exception to signal a test failure.
+   This function signals a test failure by throwing an exception.