use a generic Write instance for command output

cli/src/invocation/cmd/add.rs

@@ -1,34 +1,42 @@
 use crate::argparse::{DescriptionMod, Modification};
 use failure::Fallible;
 use taskchampion::{Replica, Status};
+use termcolor::WriteColor;
 
-pub(crate) fn execute(replica: &mut Replica, modification: Modification) -> Fallible<()> {
+pub(crate) fn execute<W: WriteColor>(
+    w: &mut W,
+    replica: &mut Replica,
+    modification: Modification,
+) -> Fallible<()> {
     let description = match modification.description {
         DescriptionMod::Set(ref s) => s.clone(),
         _ => "(no description)".to_owned(),
     };
     let t = replica.new_task(Status::Pending, description).unwrap();
-    println!("added task {}", t.get_uuid());
+    write!(w, "added task {}\n", t.get_uuid())?;
     Ok(())
 }
 
 #[cfg(test)]
 mod test {
     use super::*;
-    use crate::invocation::cmd::test::test_replica;
+    use crate::invocation::cmd::test::*;
 
     #[test]
     fn test_add() {
+        let mut w = test_writer();
         let mut replica = test_replica();
         let modification = Modification {
             description: DescriptionMod::Set("my description".to_owned()),
             ..Default::default()
         };
-        execute(&mut replica, modification).unwrap();
+        execute(&mut w, &mut replica, modification).unwrap();
 
         // check that the task appeared..
         let task = replica.get_working_set_task(1).unwrap().unwrap();
         assert_eq!(task.get_description(), "my description");
         assert_eq!(task.get_status(), Status::Pending);
+
+        assert_eq!(w.into_string(), format!("added task {}\n", task.get_uuid()));
     }
 }