diff --git a/src/day01.rs b/src/day01.rs
new file mode 100644
index 0000000..a376006
--- /dev/null
+++ b/src/day01.rs
@@ -0,0 +1,33 @@
+use crate::utils;
+use anyhow::Result;
+
+fn count_incrementing_windows(window: usize, v: &[i64]) -> usize {
+    v[window..].iter().zip(v).filter(|(b, a)| b > a).count()
+}
+
+pub(crate) fn run() -> Result<(usize, usize)> {
+    let data = utils::read_i64s("data/day01.txt")?;
+    Ok((
+        count_incrementing_windows(1, &data),
+        count_incrementing_windows(3, &data),
+    ))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_example() {
+        let data = utils::read_i64s("data/day01-test.txt").unwrap();
+        assert_eq!(count_incrementing_windows(1, &data), 7);
+        assert_eq!(count_incrementing_windows(3, &data), 5);
+    }
+
+    #[test]
+    fn test_my_data() {
+        let data = utils::read_i64s("data/day01.txt").unwrap();
+        assert_eq!(count_incrementing_windows(1, &data), 1298);
+        assert_eq!(count_incrementing_windows(3, &data), 1248);
+    }
+}
diff --git a/src/main.rs b/src/main.rs
index a22c59a..05bf281 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,35 +1,9 @@
 use anyhow::Result;
-use std::fs;
 
-fn read_i64s(filename: &str) -> Result<Vec<i64>> {
-    Ok(read_file(filename)?
-        .lines()
-        .map(|s| s.parse::<i64>().expect("i64 parse error"))
-        .collect())
-}
-
-fn read_file(filename: &str) -> Result<String> {
-    Ok(fs::read_to_string(filename)?)
-}
-
-fn count_incrementing_windows(window: usize, v: &[i64]) -> usize {
-    v[window..].iter().zip(v).filter(|(b, a)| b > a).count()
-}
-
-fn day01() -> Result<(usize, usize)> {
-    let data = read_i64s("data/day01-test.txt")?;
-    assert_eq!(count_incrementing_windows(1, &data), 7);
-    assert_eq!(count_incrementing_windows(3, &data), 5);
-
-    let data = read_i64s("data/day01.txt")?;
-    let part1 = count_incrementing_windows(1, &data);
-    let part2 = count_incrementing_windows(3, &data);
-    assert_eq!(part1, 1298);
-    assert_eq!(part2, 1248);
-    Ok((part1, part2))
-}
+mod day01;
+mod utils;
 
 fn main() -> Result<()> {
-    println!("day01: {:?}", day01()?);
+    println!("day01: {:?}", day01::run()?);
     Ok(())
 }
diff --git a/src/utils.rs b/src/utils.rs
new file mode 100644
index 0000000..898d2fd
--- /dev/null
+++ b/src/utils.rs
@@ -0,0 +1,13 @@
+use anyhow::Result;
+use std::fs;
+
+pub fn read_i64s(filename: &str) -> Result<Vec<i64>> {
+    Ok(read_file(filename)?
+        .lines()
+        .map(|s| s.parse::<i64>().expect("i64 parse error"))
+        .collect())
+}
+
+pub fn read_file(filename: &str) -> Result<String> {
+    Ok(fs::read_to_string(filename)?)
+}