Vendor dependencies

Let's see how I like this workflow.

vendor/tokio/tests/test_clock.rs

@@ -0,0 +1,50 @@
+#![warn(rust_2018_idioms)]
+#![cfg(feature = "full")]
+
+use tokio::time::{self, Duration, Instant};
+
+#[tokio::test]
+async fn resume_lets_time_move_forward_instead_of_resetting_it() {
+    let start = Instant::now();
+    time::pause();
+    time::advance(Duration::from_secs(10)).await;
+    let advanced_by_ten_secs = Instant::now();
+    assert!(advanced_by_ten_secs - start > Duration::from_secs(10));
+    assert!(advanced_by_ten_secs - start < Duration::from_secs(11));
+    time::resume();
+    assert!(advanced_by_ten_secs < Instant::now());
+    assert!(Instant::now() - advanced_by_ten_secs < Duration::from_secs(1));
+}
+
+#[tokio::test]
+async fn can_pause_after_resume() {
+    let start = Instant::now();
+    time::pause();
+    time::advance(Duration::from_secs(10)).await;
+    time::resume();
+    time::pause();
+    time::advance(Duration::from_secs(10)).await;
+    assert!(Instant::now() - start > Duration::from_secs(20));
+    assert!(Instant::now() - start < Duration::from_secs(21));
+}
+
+#[tokio::test]
+#[should_panic]
+async fn freezing_time_while_frozen_panics() {
+    time::pause();
+    time::pause();
+}
+
+#[tokio::test]
+#[should_panic]
+async fn advancing_time_when_time_is_not_frozen_panics() {
+    time::advance(Duration::from_secs(1)).await;
+}
+
+#[tokio::test]
+#[should_panic]
+async fn resuming_time_when_not_frozen_panics() {
+    time::pause();
+    time::resume();
+    time::resume();
+}