Make sure that day1/part1 is getting the correct solution again

Add input.txt for day1, add test for example case

day1/src/main.rs

@@ -1,5 +1,6 @@
 mod part1;
 
 fn main() {
-    println!("Hello, world!");
+    println!("Part1: {}", part1::main());
+    println!("Part2: TODO");
 }

day1/src/part1.rs

@@ -1,44 +1,29 @@
 use regex::Regex;
-use std::{fs::read_to_string, path::Path};
 
-fn parse(file: &str, parse_words: bool) -> i32 {
-    read_to_string(Path::new(file))
-        .unwrap()
+pub(crate) fn main() -> i32 {
+    parse(include_str!("input.txt"))
+}
+
+pub(crate) fn parse(input: &str) -> i32 {
+    input
         .lines()
-        .map(|m| calibration_values(num_from_line(m, parse_words)))
+        .map(|m| calibration_values(num_from_line(m)))
         .sum()
 }
 
-fn num_from_line(line: &str, parse_words: bool) -> Vec<i32> {
-    let rstring = if parse_words {
-        r"(\d|one|two|three|four|five|six|seven|eight|nine){1}"
-    } else {
-        r"(\d){1}"
-    };
-    Regex::new(rstring)
+pub(crate) fn num_from_line(line: &str) -> Vec<i32> {
+    Regex::new(r"(\d){1}")
         .unwrap()
         .find_iter(line)
-        .map(|m| -> i32 {
-            match m.as_str().parse::<i32>() {
-                Ok(val) => val,
-                Err(_) => match m.as_str().to_lowercase().as_ref() {
-                    "one" => 1,
-                    "two" => 2,
-                    "three" => 3,
-                    "four" => 4,
-                    "five" => 5,
-                    "six" => 6,
-                    "seven" => 7,
-                    "eight" => 8,
-                    "nine" => 9,
-                    _ => panic!("Shouldn't get here due to rstring {}", &rstring),
-                },
-            }
+        .map(|m| {
+            m.as_str()
+                .parse::<i32>()
+                .expect("Expected i32 due to Regex match")
         })
         .collect()
 }
 
-fn calibration_values(num_vec: Vec<i32>) -> i32 {
+pub(crate) fn calibration_values(num_vec: Vec<i32>) -> i32 {
     ([num_vec[0], num_vec[num_vec.len() - 1]])
         .iter()
         .fold(String::new(), |a, b| a + &b.to_string())
@@ -46,7 +31,16 @@ fn calibration_values(num_vec: Vec<i32>) -> i32 {
         .unwrap()
 }
 
-pub(crate) fn main() {
-    println!("{:?}", parse("inputs/2023/day1_1.txt", false));
-    println!("{:?}", parse("inputs/2023/test1_2.txt", true));
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn example() {
+        let input = "1abc2
+pqr3stu8vwx
+a1b2c3d4e5f
+treb7uchet";
+        assert_eq!(parse(input), 142);
+    }
 }