Added unit tests for add filter

tests/src/erlydtl_unittests.erl

@@ -366,9 +366,27 @@ tests() ->
                 {"Escape is applied last",
                     <<"{{ var1|escape|linebreaksbr }}">>, [{var1, <<"\n">>}],
                     <<"&lt;br /&gt;">>},
-                {"|add:4",
-                    <<"{{ one|add:4 }}">>, [{one, "1"}],
-                    <<"5">>},
+		{"add; lhs number, rhs number",
+		      <<"{{ one|add:4}}">>, [{one, 1}],
+		      <<"5">>},
+		{"add; lhs numeric string, rhs number",
+		      <<"{{ one|add:4}}">>, [{one, "1"}],
+		      <<"5">>},
+		{"add; lhs number, rhs numeric string",
+		      <<"{{ one|add:'4'}}">>, [{one, 1}],
+		      <<"5">>},
+		{"add; lhs non-numeric string, rhs number",
+		      <<"{{ one|add:4}}">>, [{one, "foo"}],
+		      <<"foo4">>},
+		{"add; lhs number, rhs non-numeric string",
+		      <<"{{ one|add:'foo'}}">>, [{one, 1}],
+		      <<"1foo">>},
+		{"add; lhs non-numeric string, rhs non-numeric string",
+		      <<"{{ one|add:'bar'}}">>, [{one, "foo"}],
+		      <<"foobar">>},
+		{"add; lhs numeric string, rhs numeric string",
+		      <<"{{ one|add:'4'}}">>, [{one, "1"}],
+		      <<"5">>},
                 {"|addslashes",
                     <<"{{ var1|addslashes }}">>, [{var1, "Jimmy's \"great\" meats'n'things"}],
                     <<"Jimmy\\'s \\\"great\\\" meats\\'n\\'things">>},