diff --git a/src/population.rs b/src/population.rs
index 096cab1..1ae1bba 100644
--- a/src/population.rs
+++ b/src/population.rs
@@ -424,11 +424,19 @@ mod tests {
         let mut population: Population;
         let mut stats: Stats;
         let (width, height) = (100, 100);
+        let start_infected = 50;
 
         disease = Disease::new(infection_rate, 0, 0, String::from("Test"));
-        population = Population::new(50, 0, 0, width, height, disease);
+        population = Population::new(start_infected, 0, 0, width, height, disease);
         stats = humans_stats(&population.humans);
         println!("Population: {:?}", stats);
+
+        // total * proba - 20% < infected < total * proba + 20%
+        let expected_infected = width * height * start_infected as i32 / 100;
+        let tolerance = ((width * height) as f32 * 0.2) as i32;
+        assert!(stats.infected < expected_infected + tolerance);
+        assert!(stats.infected > expected_infected - tolerance);
+
         population.generate();
         population.propagate();
         stats = humans_stats(&population.humans);