add new render tests that exercise zombie handling

tests/render.rs

@@ -650,3 +650,127 @@ fn progress_style_tab_width_unification() {
     spinner.tick();
     assert_eq!(in_mem.contents(), "OK    OK");
 }
+
+#[test]
+fn multi_progress_clear_println() {
+    let in_mem = InMemoryTerm::new(10, 80);
+    let mp =
+        MultiProgress::with_draw_target(ProgressDrawTarget::term_like(Box::new(in_mem.clone())));
+
+    mp.println("Test of println").unwrap();
+    // Should have no effect
+    mp.clear().unwrap();
+    assert_eq!(in_mem.contents(), "Test of println");
+}
+
+#[test]
+fn multi_progress_clear_zombies_no_ticks() {
+    _multi_progress_clear_zombies(0);
+}
+
+#[test]
+fn multi_progress_clear_zombies_one_tick() {
+    _multi_progress_clear_zombies(1);
+}
+
+#[test]
+fn multi_progress_clear_zombies_two_ticks() {
+    _multi_progress_clear_zombies(2);
+}
+
+// In the old (broken) implementation, zombie handling sometimes worked differently depending on
+// how many draws were between certain operations. Let's make sure that doesn't happen again.
+fn _multi_progress_clear_zombies(ticks: usize) {
+    let in_mem = InMemoryTerm::new(10, 80);
+    let mp =
+        MultiProgress::with_draw_target(ProgressDrawTarget::term_like(Box::new(in_mem.clone())));
+    let style = ProgressStyle::with_template("{msg}").unwrap();
+
+    let pb1 = mp.add(
+        ProgressBar::new_spinner()
+            .with_style(style.clone())
+            .with_message("pb1"),
+    );
+    pb1.tick();
+
+    let pb2 = mp.add(
+        ProgressBar::new_spinner()
+            .with_style(style)
+            .with_message("pb2"),
+    );
+
+    pb2.tick();
+    assert_eq!(in_mem.contents(), "pb1\npb2");
+
+    pb1.finish_with_message("pb1 done");
+    drop(pb1);
+    assert_eq!(in_mem.contents(), "pb1 done\npb2");
+
+    for _ in 0..ticks {
+        pb2.tick();
+    }
+
+    mp.clear().unwrap();
+    assert_eq!(in_mem.contents(), "");
+}
+
+// This test reproduces examples/multi.rs in a simpler form
+#[test]
+fn multi_zombie_handling() {
+    let in_mem = InMemoryTerm::new(10, 80);
+    let mp =
+        MultiProgress::with_draw_target(ProgressDrawTarget::term_like(Box::new(in_mem.clone())));
+    let style = ProgressStyle::with_template("{msg}").unwrap();
+
+    let pb1 = mp.add(
+        ProgressBar::new_spinner()
+            .with_style(style.clone())
+            .with_message("pb1"),
+    );
+    pb1.tick();
+    let pb2 = mp.add(
+        ProgressBar::new_spinner()
+            .with_style(style.clone())
+            .with_message("pb2"),
+    );
+    pb2.tick();
+    let pb3 = mp.add(
+        ProgressBar::new_spinner()
+            .with_style(style)
+            .with_message("pb3"),
+    );
+    pb3.tick();
+
+    mp.println("pb1 done!").unwrap();
+    pb1.finish_with_message("done");
+    assert_eq!(in_mem.contents(), "pb1 done!\ndone\npb2\npb3");
+    drop(pb1);
+
+    assert_eq!(in_mem.contents(), "pb1 done!\ndone\npb2\npb3");
+
+    pb2.tick();
+    assert_eq!(in_mem.contents(), "pb1 done!\ndone\npb2\npb3");
+    pb3.tick();
+    assert_eq!(in_mem.contents(), "pb1 done!\ndone\npb2\npb3");
+
+    mp.println("pb3 done!").unwrap();
+    assert_eq!(in_mem.contents(), "pb1 done!\npb3 done!\npb2\npb3");
+
+    pb3.finish_with_message("done");
+    drop(pb3);
+
+    pb2.tick();
+
+    mp.println("pb2 done!").unwrap();
+    pb2.finish_with_message("done");
+    drop(pb2);
+
+    assert_eq!(
+        in_mem.contents(),
+        "pb1 done!\npb3 done!\npb2 done!\ndone\ndone"
+    );
+
+    mp.clear().unwrap();
+
+    assert_eq!(in_mem.contents(), "pb1 done!\npb3 done!\npb2 done!");
+}