ADD unit tests for sample line

 - small fix to sample line
 - added two unit test
 - extracted sample_line into new file

src/main.rs

@@ -7,6 +7,7 @@ use core::time;
 
 
 mod app;
+mod plotting_utils;
 mod widget_progress_bar;
 mod widget_main_chart;
 mod widget_text_output;

src/plotting_utils.rs

@@ -0,0 +1,35 @@
+pub fn sample_line(a: f64, b: f64, min: (f64, f64), max: (f64, f64), sample_rate: f64) -> Vec<(f64, f64)> {
+    let mut x = min.0;
+    let mut sampled_line: Vec<(f64, f64)> = vec![];
+
+    while x < max.0 {
+        sampled_line.push((x, a * x + b));
+        x += sample_rate;
+    }
+
+    sampled_line
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_sample_horizontal_line() {
+        let line = sample_line(0.0, 42.0, (0.0, 0.0), (100.0, 100.0), 0.1);
+
+        assert_eq!(line.len(), 1001, "not the good number of samples");
+        assert_eq!((line[0].0.round(), line[0].1.round()), (0.0, 42.0));
+        assert_eq!((line[10].0.round(), line[10].1.round()), (1.0, 42.0));
+        assert_eq!((line[1000].0.round(), line[1000].1.round()), (100.0, 42.0));
+    }
+
+    #[test]
+    fn test_sample_vertical_line() {
+        let line = sample_line(std::f64::MAX, 0.0, (0.0, 0.0), (100.0, 100.0), 0.1);
+
+        assert_eq!(line.len(), 1001, "not the good number of samples");
+        assert_eq!(line[0], (0.0, 0.0));
+        assert_eq!((line[1000].0.round(), line[1000].1.round()), (100.0, std::f64::INFINITY));
+    }
+}

src/widget_main_chart.rs

@@ -4,20 +4,9 @@ use termion::raw::RawTerminal;
 use std::io::Stdout;
 use tui::widgets::{Dataset, Marker, Chart, Block, Axis, Widget};
 use tui::style::{Style, Color};
+use crate::plotting_utils::sample_line;
 
-const SAMPLE_RATE: f64 = 0.1;
-
-fn sample_line(a: f64, b: f64, min: (f64, f64), max: (f64, f64), sample_rate: f64) -> Vec<(f64, f64)> {
-    let mut x = min.0;
-    let mut sampled_line: Vec<(f64, f64)> = vec![];
-
-    while x < max.0 {
-        x += sample_rate;
-        sampled_line.push((x, a * x + b));
-    }
-
-    sampled_line
-}
+const SAMPLE_RATE: f64 = 0.01;
 
 pub fn main_chart(frame: &mut Frame<TermionBackend<RawTerminal<Stdout>>>,
                   regression: (f64, f64),