diff --git a/Cargo.toml b/Cargo.toml
index b5d70a3..c1e3a53 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -11,3 +11,6 @@ ndarray = "*"
 thiserror = "*"
 rand = "*"
 bimap = "*"
+
+[dev-dependencies]
+approx = "*"
diff --git a/src/lib.rs b/src/lib.rs
index ee48d80..b2e9365 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,3 +1,7 @@
+#[cfg(test)]
+#[macro_use]
+extern crate approx;
+
 pub mod node;
 pub mod params;
 pub mod network;
diff --git a/src/params.rs b/src/params.rs
index f3793a3..8825e86 100644
--- a/src/params.rs
+++ b/src/params.rs
@@ -3,6 +3,7 @@ use std::collections::{HashMap, BTreeSet};
 use rand::Rng;
 use thiserror::Error;
 
+
 #[derive(Error, Debug)]
 pub enum ParamsError {
     #[error("Unsupported method")]
@@ -73,21 +74,22 @@ impl Params for DiscreteStatesContinousTimeParams {
            Option::Some(cim) => {   
             let mut rng = rand::thread_rng();
             let lambda = cim[[u, state, state]] * -1.0;
-            let x = rng.gen_range(0.0..1.0);
+            let x: f64 = rng.gen_range(0.0..1.0);
 
-            let state = (cim.slice(s![u,state,..])).iter().scan((0, 0.0), |acc, &x| {
-                if x > 0.0 && acc.1 < x {
-                    acc.0 += 1;
+            let next_state = cim.slice(s![u,state,..]).map(|x| x / lambda).iter().fold((0, 0.0), |mut acc, ele| { 
+                if &acc.1 + ele < x  && ele > &0.0{
                     acc.1 += x;
-                    return Some(*acc);
-                } else if acc.1 < x {
                     acc.0 += 1;
-                    return Some(*acc);
-                }
-                None
+                }                
+                acc});
+
+            let next_state = if next_state.0 < state {
+                next_state.0
+            } else {
+                next_state.0 + 1
+            };
 
-            }).last();
-            Ok(StateType::Discrete(state.unwrap().0))
+            Ok(StateType::Discrete(next_state as u32))
             
            },
            Option::None => Err(ParamsError::ParametersNotInitialized(String::from("CIM not initialized")))
@@ -105,3 +107,70 @@ impl Params for DiscreteStatesContinousTimeParams {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use ndarray::prelude::*;
+
+
+    fn create_ternary_discrete_time_continous_param() -> DiscreteStatesContinousTimeParams {
+        let mut domain = BTreeSet::new();
+        domain.insert(String::from("A"));
+        domain.insert(String::from("B"));
+        domain.insert(String::from("C"));
+        let mut params = DiscreteStatesContinousTimeParams::init(domain);
+
+        let cim = array![
+            [
+                [-3.0, 2.0, 1.0],
+                [1.0, -5.0, 4.0],
+                [3.2, 1.7, -4.0]
+            ]];
+
+        params.cim = Some(cim);
+        params
+    }
+    
+    #[test]
+    fn test_uniform_generation() {
+        let param = create_ternary_discrete_time_continous_param();
+        let mut states = Array1::<u32>::zeros(10000);
+
+        states.mapv_inplace(|_| if let StateType::Discrete(val) = param.get_random_state_uniform() {
+            val
+        } else {panic!()});
+        let zero_freq = states.mapv(|a| (a == 0) as u64).sum() as f64 / 10000.0;
+
+        assert_relative_eq!(1.0/3.0, zero_freq, epsilon=0.01);
+    }
+
+
+    #[test]
+    fn test_random_generation_state() {
+        let param = create_ternary_discrete_time_continous_param();
+        let mut states = Array1::<u32>::zeros(10000);
+
+        states.mapv_inplace(|_| if let StateType::Discrete(val) = param.get_random_state(1, 0).unwrap() {
+            val
+        } else {panic!()});
+        let two_freq = states.mapv(|a| (a == 2) as u64).sum() as f64 / 10000.0;
+        let zero_freq = states.mapv(|a| (a == 0) as u64).sum() as f64 / 10000.0;
+
+        assert_relative_eq!(4.0/5.0, two_freq, epsilon=0.01);
+        assert_relative_eq!(1.0/5.0, zero_freq, epsilon=0.01);
+    }
+
+    
+    #[test]
+    fn test_random_generation_residence_time() {
+        let param = create_ternary_discrete_time_continous_param();
+        let mut states = Array1::<f64>::zeros(10000);
+
+        states.mapv_inplace(|_| param.get_random_residence_time(1, 0).unwrap() );
+
+        assert_relative_eq!(1.0/5.0, states.mean().unwrap(), epsilon=0.01);
+
+    }
+
+}