Move lexer tests to a #[cfg(test)] mod tests { } modules

src/lexer/mod.rs

@@ -192,6 +192,12 @@ impl Iterator for Lexer {
 // UNIT TESTING
 //
 
+#[cfg(test)]
+mod tests {
+    use std::iter::Iterator;
+    use super::*;
+    use super::token::*;
+
     #[test]
     fn lexer_finds_parens() {
         let mut lexer = Lexer::new("()");
@@ -232,3 +238,4 @@ fn assert_next_token(lexer: &mut Lexer, expected: &Token) {
         let lex = lexer.next().unwrap();
         assert_eq!(lex.token, *expected);
     }
+}