use a generic Write instance for command output

cli/src/invocation/cmd/modify.rs

@@ -2,8 +2,10 @@ use crate::argparse::{Filter, Modification};
 use crate::invocation::{apply_modification, filtered_tasks};
 use failure::Fallible;
 use taskchampion::Replica;
+use termcolor::WriteColor;
 
-pub(crate) fn execute(
+pub(crate) fn execute<W: WriteColor>(
+    w: &mut W,
     replica: &mut Replica,
     filter: Filter,
     modification: Modification,
@@ -11,7 +13,7 @@ pub(crate) fn execute(
     for task in filtered_tasks(replica, &filter)? {
         let mut task = task.into_mut(replica);
 
-        apply_modification(&mut task, &modification)?;
+        apply_modification(w, &mut task, &modification)?;
     }
 
     Ok(())
@@ -22,10 +24,12 @@ mod test {
     use super::*;
     use crate::argparse::DescriptionMod;
     use crate::invocation::cmd::test::test_replica;
+    use crate::invocation::cmd::test::*;
     use taskchampion::Status;
 
     #[test]
     fn test_modify() {
+        let mut w = test_writer();
         let mut replica = test_replica();
 
         let task = replica
@@ -39,11 +43,16 @@ mod test {
             description: DescriptionMod::Set("new description".to_owned()),
             ..Default::default()
         };
-        execute(&mut replica, filter, modification).unwrap();
+        execute(&mut w, &mut replica, filter, modification).unwrap();
 
         // check that the task appeared..
         let task = replica.get_task(task.get_uuid()).unwrap().unwrap();
         assert_eq!(task.get_description(), "new description");
         assert_eq!(task.get_status(), Status::Pending);
+
+        assert_eq!(
+            w.into_string(),
+            format!("modified task {}\n", task.get_uuid())
+        );
     }
 }