Improvements to code coverage:

More tests and test cases are added to bring up
the percentage of library code covered by tests.

test/websocket/error.cpp

@@ -7,3 +7,45 @@
 
 // Test that header file is self-contained.
 #include <beast/websocket/error.hpp>
+
+#include <beast/unit_test/suite.hpp>
+#include <memory>
+
+namespace beast {
+namespace websocket {
+
+class error_test : public unit_test::suite
+{
+public:
+    void check(char const* name, error ev)
+    {
+        auto const ec = make_error_code(ev);
+        expect(std::string{ec.category().name()} == name);
+        expect(! ec.message().empty());
+        expect(std::addressof(ec.category()) ==
+            std::addressof(detail::get_error_category()));
+        expect(detail::get_error_category().equivalent(static_cast<int>(ev),
+            ec.category().default_error_condition(static_cast<int>(ev))));
+        expect(detail::get_error_category().equivalent(
+            ec, static_cast<int>(ev)));
+    }
+
+    void run() override
+    {
+        check("websocket", error::closed);
+        check("websocket", error::failed);
+        check("websocket", error::handshake_failed);
+        check("websocket", error::keep_alive);
+        check("websocket", error::response_malformed);
+        check("websocket", error::response_failed);
+        check("websocket", error::response_denied);
+        check("websocket", error::request_malformed);
+        check("websocket", error::request_invalid);
+        check("websocket", error::request_denied);
+    }
+};
+
+BEAST_DEFINE_TESTSUITE(error,websocket,beast);
+
+} // http
+} // beast