add test for harmless disease

src/population.rs

@@ -47,7 +47,7 @@ impl Population {
             for y in 0..height {
                 let idx = human_idx(x, y, width);
                 let mut present_state = State::Normal;
-                if (start_infected_ratio) > 0
+                if (start_infected_ratio > 0)
                     && (rng.gen_range(0..CORRECTED_PERCENTAGE) <= start_infected_ratio)
                 {
                     present_state = State::Infected;
@@ -643,6 +643,27 @@ mod tests {
         }
     }
 
+    #[parameterized(infection_start = {0, 50, 100})]
+    fn propagate_harmless(infection_start: i32) {
+        let disease: Disease = Disease::new(0, 0, 0, String::from("Harmless"));
+        let (width, height) = (100, 100);
+        let mut population: Population = Population::new(infection_start, 0, 0, width, height, disease);
+        let stats_before: Stats;
+        let stats_after: Stats;
+
+        stats_before = humans_stats(&population.humans);
+        let should_be_infected = population.size as i32 * infection_start / 100;
+        let tolerance = (should_be_infected as f32 * 0.20) as i32;
+        println!("{:?}", stats_before);
+        assert!(stats_before.infected <= should_be_infected + tolerance, "{} infected, should be less than {}", stats_before.infected, should_be_infected + tolerance);
+        assert!(stats_before.infected >= should_be_infected - tolerance, "{} infected, should be more than {}", stats_before.infected, should_be_infected - tolerance);
+
+        population.propagate();
+
+        stats_after = humans_stats(&population.humans);
+        assert_eq!(stats_before.infected, stats_after.infected, "no one should have been infected");
+    }
+
     #[parameterized(infection_rate = {0, 100, 0}, death_rate = {0, 0, 100}, infected_expected = {0, 1, 0})]
     fn propagate_test(infection_rate: i32, death_rate: i32, infected_expected: i32) {
         let disease: Disease;