use a generic Write instance for command output

cli/src/invocation/cmd/sync.rs

@@ -1,26 +1,32 @@
 use failure::Fallible;
 use taskchampion::{server::Server, Replica};
+use termcolor::WriteColor;
 
-pub(crate) fn execute(replica: &mut Replica, server: &mut Box<dyn Server>) -> Fallible<()> {
+pub(crate) fn execute<W: WriteColor>(
+    w: &mut W,
+    replica: &mut Replica,
+    server: &mut Box<dyn Server>,
+) -> Fallible<()> {
     replica.sync(server)?;
-    println!("sync complete.");
+    write!(w, "sync complete.\n")?;
     Ok(())
 }
 
 #[cfg(test)]
 mod test {
     use super::*;
-    use crate::invocation::cmd::test::{test_replica, test_server};
+    use crate::invocation::cmd::test::*;
     use tempdir::TempDir;
 
     #[test]
     fn test_add() {
+        let mut w = test_writer();
         let mut replica = test_replica();
         let server_dir = TempDir::new("test").unwrap();
         let mut server = test_server(&server_dir);
 
-        // this just has to not fail -- the details of the actual sync are
-        // tested thoroughly in the taskchampion crate
-        execute(&mut replica, &mut server).unwrap();
+        // Note that the details of the actual sync are tested thoroughly in the taskchampion crate
+        execute(&mut w, &mut replica, &mut server).unwrap();
+        assert_eq!(&w.into_string(), "sync complete.\n")
     }
 }