diff --git a/src/interpreter.rs b/src/interpreter.rs
index f02e93e..bb4b5c6 100644
--- a/src/interpreter.rs
+++ b/src/interpreter.rs
@@ -12,16 +12,25 @@ pub enum Value {
     String(Rc<String>),
 }
 
+#[derive(Default)]
 pub struct Interpreter {
+    capture_output: bool,
+    output: Vec<Value>,
     // Variable table stores the runtime values of variables
     vartable: HashMap<String, Value>,
 }
 
 impl Interpreter {
     pub fn new() -> Self {
-        Self {
-            vartable: HashMap::new(),
-        }
+        Self::default()
+    }
+
+    pub fn set_capture_output(&mut self, enabled: bool) {
+        self.capture_output = enabled;
+    }
+
+    pub fn output(&self) -> &[Value] {
+        &self.output
     }
 
     pub fn run_str(&mut self, code: &str, print_tokens: bool, print_ast: bool) {
@@ -62,7 +71,12 @@ impl Interpreter {
 
                 Statement::Print(expr) => {
                     let result = self.resolve_expr(expr);
-                    print!("{}", result);
+
+                    if self.capture_output {
+                        self.output.push(result)
+                    } else {
+                        print!("{}", result);
+                    }
                 }
 
                 Statement::If(If {
diff --git a/src/lib.rs b/src/lib.rs
index d0fca0c..08bb042 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,5 +1,96 @@
-pub mod lexer;
-pub mod token;
-pub mod parser;
 pub mod ast;
 pub mod interpreter;
+pub mod lexer;
+pub mod parser;
+pub mod token;
+
+#[cfg(test)]
+mod tests {
+    use crate::interpreter::{Interpreter, Value};
+    use std::fs::read_to_string;
+
+    #[test]
+    fn test_euler1() {
+        let filename = "euler1.nek";
+        let correct_result = 233168;
+
+        let mut interpreter = Interpreter::new();
+        interpreter.set_capture_output(true);
+
+        let code = read_to_string(format!("examples/{filename}")).unwrap();
+
+        interpreter.run_str(&code, false, false);
+
+        let expected_output = [Value::I64(correct_result)];
+
+        assert_eq!(interpreter.output(), &expected_output);
+    }
+
+    #[test]
+    fn test_euler2() {
+        let filename = "euler2.nek";
+        let correct_result = 4613732;
+
+        let mut interpreter = Interpreter::new();
+        interpreter.set_capture_output(true);
+
+        let code = read_to_string(format!("examples/{filename}")).unwrap();
+
+        interpreter.run_str(&code, false, false);
+
+        let expected_output = [Value::I64(correct_result)];
+
+        assert_eq!(interpreter.output(), &expected_output);
+    }
+
+    #[test]
+    fn test_euler3() {
+        let filename = "euler3.nek";
+        let correct_result = 6857;
+
+        let mut interpreter = Interpreter::new();
+        interpreter.set_capture_output(true);
+
+        let code = read_to_string(format!("examples/{filename}")).unwrap();
+
+        interpreter.run_str(&code, false, false);
+
+        let expected_output = [Value::I64(correct_result)];
+
+        assert_eq!(interpreter.output(), &expected_output);
+    }
+
+    #[test]
+    fn test_euler4() {
+        let filename = "euler4.nek";
+        let correct_result = 906609;
+
+        let mut interpreter = Interpreter::new();
+        interpreter.set_capture_output(true);
+
+        let code = read_to_string(format!("examples/{filename}")).unwrap();
+
+        interpreter.run_str(&code, false, false);
+
+        let expected_output = [Value::I64(correct_result)];
+
+        assert_eq!(interpreter.output(), &expected_output);
+    }
+
+    #[test]
+    fn test_euler5() {
+        let filename = "euler5.nek";
+        let correct_result = 232792560;
+
+        let mut interpreter = Interpreter::new();
+        interpreter.set_capture_output(true);
+
+        let code = read_to_string(format!("examples/{filename}")).unwrap();
+
+        interpreter.run_str(&code, false, false);
+
+        let expected_output = [Value::I64(correct_result)];
+
+        assert_eq!(interpreter.output(), &expected_output);
+    }
+}