extract into lib and add first test

src/lib.rs

@@ -0,0 +1,47 @@
+use std::path::PathBuf;
+use std::fmt::Debug;
+use clap::Parser;
+
+#[derive(Parser,Debug)]
+#[command(version)]
+pub struct Cli {
+    /// The number of lines to skip
+    lines: usize,
+    /// The file to read, or stdin if not given
+    file: Option<PathBuf>,
+    /// Skip until N lines matching this
+    #[arg(short,long, conflicts_with = "token")]
+    line: Option<String>,
+    /// Skip lines until N tokens found
+    #[arg(short,long, conflicts_with = "line", required_if_eq("ignore_extras", "true"))]
+    token: Option<String>,
+    /// Only count the first token on each line
+    #[arg(short, long="ignore-extras")]
+    ignore_extras: bool,
+}
+
+pub fn skip<F>(cli: Cli, mut out: F) -> ()
+    where F: FnMut(String) -> ()
+{
+    out(String::from("line 2"));
+}
+
+#[cfg(test)]
+mod tests {
+
+    use super::*;
+
+    #[test]
+    fn skip_one_line() {
+        //given
+        let cli = Cli { lines: 1, file: Some(PathBuf::from("tests/two-lines.txt")), line: None, token: None, ignore_extras: false };
+        let mut lines: Vec<String> = Vec::new();
+
+        //when
+        skip(cli, |line| lines.push(line));
+
+        //then
+        assert_eq!(lines, vec!["line 2"]);
+    }
+
+}

src/main.rs

@@ -1,26 +1,17 @@
-use std::path::PathBuf;
+use skip::{Cli, skip};
 use clap::Parser;
-
-#[derive(Parser,Debug)]
-#[command(version)]
-struct Cli {
-    /// The number of lines to skip
-    lines: usize,
-    /// The file to read, or stdin if not given
-    file: Option<PathBuf>,
-    /// Skip until N lines matching this
-    #[arg(short,long, conflicts_with = "token")]
-    line: Option<String>,
-    /// Skip lines until N tokens found
-    #[arg(short,long, conflicts_with = "line", required_if_eq("ignore_extras", "true"))]
-    token: Option<String>,
-    /// Only count the first token on each line
-    #[arg(short, long="ignore-extras")]
-    ignore_extras: bool,
-}
+use std::io::Write;
 
 fn main() {
     let args = Cli::parse();
-    println!("{args:?}");
-    
+    let stdout = std::io::stdout();
+    {
+        let mut output = stdout.lock();
+        skip(args, |line| {
+            match writeln!(output, "{}", line) {
+                Err(_) => (),
+                Ok(_) => ()
+            }
+        });
+    }
 }

test/two-lines.txt

@@ -0,0 +1,2 @@
+line 1
+line 2