diff --git a/src/main.rs b/src/main.rs
index 2b2f784..b3974d3 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -30,3 +30,54 @@ fn main() {
     buffer.clear();
   }
 }
+
+
+#[cfg(test)]
+mod tests {
+  use crate::*;
+
+  fn calc(task: &str) -> i32 {
+    return eval(to_rpn(tokenizer(task)));
+  }
+
+  #[test]
+  fn alg_order() {
+    assert_eq!(calc("2 + 3 * 4"), 14);
+  }
+
+  #[test]
+  fn left_sub_assoc() {
+    assert_eq!(calc("8 - 4 - 2"), 2);
+  }
+
+  #[test]
+  fn left_div_assoc() {
+    assert_eq!(calc("100 / 5 / 2"), 10);
+  }
+
+
+  #[test]
+  fn br_1() {
+    assert_eq!(calc("(2 + 3) * 4"), 20);
+  }
+
+  #[test]
+  fn br_2() {
+    assert_eq!(calc("(3 + 5) * (2 - 1)"), 8);
+  }
+
+  #[test]
+  fn br_3() {
+    assert_eq!(calc("(2 + (3 * (4 + 1)))"), 17);
+  }
+
+  #[test]
+  fn br_4() {
+    assert_eq!(calc("((((1+2)+3)+4)+5)"), 15);
+  }
+
+  #[test]
+  fn br_5() {
+    assert_eq!(calc("(1 + 2) * (3 + 4 * (5 + 6))"), 141);
+  }
+}
diff --git a/src/tokenizer.rs b/src/tokenizer.rs
index 24231b8..57bc7e4 100644
--- a/src/tokenizer.rs
+++ b/src/tokenizer.rs
@@ -47,3 +47,183 @@ pub fn tokenizer(task: &str) -> Vec<Token> {
 
   return tokens;
 }
+
+
+#[cfg(test)]
+mod tests {
+  use super::*;
+
+  #[test]
+  fn test_addition() {
+    assert_eq!(
+      tokenizer("2+3"),
+      vec![Token::Number(2), Token::Addition, Token::Number(3)]
+    );
+  }
+
+  #[test]
+  fn test_subtraction() {
+    assert_eq!(
+      tokenizer("5-7"),
+      vec![Token::Number(5), Token::Substruction, Token::Number(7)]
+    );
+  }
+
+  #[test]
+  fn test_multiplication() {
+    assert_eq!(
+      tokenizer("4*9"),
+      vec![Token::Number(4), Token::Multiplication, Token::Number(9)]
+    );
+  }
+
+  #[test]
+  fn test_division() {
+    assert_eq!(
+      tokenizer("10/2"),
+      vec![Token::Number(10), Token::Division, Token::Number(2)]
+    );
+  }
+
+  #[test]
+  fn test_brackets() {
+    assert_eq!(
+      tokenizer("(1+2)"),
+      vec![
+        Token::BracketOpen,
+        Token::Number(1),
+        Token::Addition,
+        Token::Number(2),
+        Token::BracketClose
+      ]
+    );
+  }
+
+  #[test]
+  fn test_nested_brackets() {
+    assert_eq!(
+      tokenizer("((3+4)*2)"),
+      vec![
+        Token::BracketOpen,
+        Token::BracketOpen,
+        Token::Number(3),
+        Token::Addition,
+        Token::Number(4),
+        Token::BracketClose,
+        Token::Multiplication,
+        Token::Number(2),
+        Token::BracketClose
+      ]
+    );
+  }
+
+  #[test]
+  fn test_multidigit_numbers() {
+    assert_eq!(
+      tokenizer("123+456"),
+      vec![Token::Number(123), Token::Addition, Token::Number(456)]
+    );
+  }
+
+  #[test]
+  fn test_large_number_within_i32() {
+    assert_eq!(
+      tokenizer("2147483647"),
+      vec![Token::Number(2147483647)]
+    );
+  }
+
+  #[test]
+  #[should_panic(expected = "attempt to parse integer")]
+  fn test_number_out_of_i32_range() {
+    tokenizer("2147483648");
+  }
+
+  #[test]
+  fn test_ignore_spaces() {
+    assert_eq!(
+      tokenizer(" 1  +  2 "),
+      vec![Token::Number(1), Token::Addition, Token::Number(2)]
+    );
+  }
+
+  #[test]
+  fn test_tabs_and_newlines_ignored() {
+    assert_eq!(
+      tokenizer("1\t+\n2"),
+      vec![Token::Number(1), Token::Addition, Token::Number(2)]
+    );
+  }
+
+  #[test]
+  fn test_unknown_characters_ignored() {
+    assert_eq!(
+      tokenizer("2@3?4"),
+      vec![Token::Number(2), Token::Number(3), Token::Number(4)]
+    );
+  }
+
+  #[test]
+  fn test_only_unknown_characters() {
+    assert_eq!(tokenizer("@#$%"), vec![]);
+  }
+
+  #[test]
+  fn test_empty_string() {
+    assert_eq!(tokenizer(""), vec![]);
+  }
+
+  #[test]
+  fn test_unary_minus() {
+    assert_eq!(
+      tokenizer("-5"),
+      vec![Token::Substruction, Token::Number(5)]
+    );
+  }
+
+  #[test]
+  fn test_expression_with_unary_minus() {
+    assert_eq!(
+      tokenizer("3+-2"),
+      vec![
+        Token::Number(3),
+        Token::Addition,
+        Token::Substruction,
+        Token::Number(2)
+      ]
+    );
+  }
+
+  #[test]
+  fn test_consecutive_operators() {
+    assert_eq!(
+      tokenizer("5*-3"),
+      vec![
+        Token::Number(5),
+        Token::Multiplication,
+        Token::Substruction,
+        Token::Number(3)
+      ]
+    );
+  }
+
+  #[test]
+  fn test_complex_expression_no_spaces() {
+    assert_eq!(
+      tokenizer("12+34*(56-78)/90"),
+      vec![
+        Token::Number(12),
+        Token::Addition,
+        Token::Number(34),
+        Token::Multiplication,
+        Token::BracketOpen,
+        Token::Number(56),
+        Token::Substruction,
+        Token::Number(78),
+        Token::BracketClose,
+        Token::Division,
+        Token::Number(90)
+      ]
+    );
+  }
+}