use a generic Write instance for command output

cli/src/invocation/cmd/list.rs

@@ -4,8 +4,13 @@ use crate::table;
 use failure::Fallible;
 use prettytable::{cell, row, Table};
 use taskchampion::Replica;
+use termcolor::WriteColor;
 
-pub(crate) fn execute(replica: &mut Replica, report: Report) -> Fallible<()> {
+pub(crate) fn execute<W: WriteColor>(
+    w: &mut W,
+    replica: &mut Replica,
+    report: Report,
+) -> Fallible<()> {
     let mut t = Table::new();
     t.set_format(table::format());
     t.set_titles(row![b->"id", b->"act", b->"description"]);
@@ -21,7 +26,7 @@ pub(crate) fn execute(replica: &mut Replica, report: Report) -> Fallible<()> {
         };
         t.add_row(row![id, active, task.get_description()]);
     }
-    t.printstd();
+    t.print(w)?;
     Ok(())
 }
 
@@ -29,17 +34,23 @@ pub(crate) fn execute(replica: &mut Replica, report: Report) -> Fallible<()> {
 mod test {
     use super::*;
     use crate::argparse::Filter;
-    use crate::invocation::cmd::test::test_replica;
+    use crate::invocation::cmd::test::*;
+    use taskchampion::Status;
 
     #[test]
     fn test_list() {
+        let mut w = test_writer();
         let mut replica = test_replica();
+        replica
+            .new_task(Status::Pending, "my task".to_owned())
+            .unwrap();
+
         let report = Report {
             filter: Filter {
                 ..Default::default()
             },
         };
-        execute(&mut replica, report).unwrap();
-        // output is to stdout, so this is as much as we can check
+        execute(&mut w, &mut replica, report).unwrap();
+        assert!(w.into_string().contains("my task"));
     }
 }