added unittests for the functionality sofar

src/main.rs

@@ -6,6 +6,9 @@ use std::process;
 mod scanner;
 mod tokens;
 
+#[cfg(test)]
+mod tests;
+
 /// main
 /// no arguments: run interactively
 /// 1 argument: run the script file specified

src/tests.rs

@@ -0,0 +1,39 @@
+#[cfg(test)]
+use crate::scanner::scan_tokens;
+use crate::tokens::TokenType::*;
+
+#[test]
+fn test_scan_empty_source() {
+    let tokens = scan_tokens("").unwrap();
+    assert_eq!(tokens.len(), 1);
+
+    let token = tokens.get(0).unwrap();
+    assert_eq!(token.token_type, EOF);
+    assert_eq!(token.line, 1);
+}
+
+#[test]
+fn test_scan_single_char_tokens() {
+    let tokens = scan_tokens(">").unwrap();
+    assert_eq!(tokens.len(), 2);
+
+    let token = tokens.get(0).unwrap();
+    assert_eq!(token.token_type, GREATER);
+    assert_eq!(token.lexeme, ">");
+
+    let token = tokens.get(1).unwrap();
+    assert_eq!(token.token_type, EOF);
+}
+
+#[test]
+fn test_scan_double_char_tokens() {
+    let tokens = scan_tokens(">=").unwrap();
+    assert_eq!(tokens.len(), 2);
+
+    let token = tokens.get(0).unwrap();
+    assert_eq!(token.token_type, GREATEREQUAL);
+    assert_eq!(token.lexeme, ">=");
+
+    let token = tokens.get(1).unwrap();
+    assert_eq!(token.token_type, EOF);
+}

src/tokens.rs

@@ -31,7 +31,7 @@ impl fmt::Debug for Token<'_> {
     }
 }
 
-#[derive(Debug, Clone, Copy)]
+#[derive(Eq, PartialEq, Debug, Clone, Copy)]
 pub enum TokenType {
     // Single-character tokens.
     LEFTPAREN,  // (