Provide matched text to lexer user code block

spec/test_lexer_match_text.d

@@ -0,0 +1,15 @@
+import testparser;
+import std.stdio;
+
+int main()
+{
+    return 0;
+}
+
+unittest
+{
+    string input = `identifier_123`;
+    auto parser = new Testparser.Parser(input);
+    assert(parser.parse() == true);
+    writeln("pass1");
+}