1 files changed, 46 insertions, 0 deletions
diff --git a/third_party/rust/instant/tests/wasm.rs b/third_party/rust/instant/tests/wasm.rs
new file mode 100644
index 0000000000..b1577adfa8
--- /dev/null
+++ b/third_party/rust/instant/tests/wasm.rs
@@ -0,0 +1,46 @@
+extern crate wasm_bindgen_test;
+
+use instant::Instant;
+use std::time::Duration;
+use wasm_bindgen_test::*;
+
+wasm_bindgen_test_configure!(run_in_browser);
+// run these tests using: wasm-pack test --chrome --headless -- --features wasm-bindgen
+
+#[wasm_bindgen_test]
+fn test_instant_now() {
+    let now = Instant::now();
+    assert!(now.elapsed().as_nanos() > 0);
+}
+
+#[wasm_bindgen_test]
+fn test_duration() {
+    let now = Instant::now();
+    let one_sec = Duration::from_secs(1);
+    assert!(now.elapsed() < one_sec);
+}
+
+// Duration::new will overflow when you have u64::MAX seconds and one billion nanoseconds.
+// <https://doc.rust-lang.org/std/time/struct.Duration.html#method.new>
+const ONE_BILLION: u32 = 1_000_000_000;
+
+#[wasm_bindgen_test]
+fn test_checked_add() {
+    let now = Instant::now();
+
+    assert!(now.checked_add(Duration::from_millis(1)).is_some());
+    assert_eq!(
+        None,
+        now.checked_add(Duration::new(u64::MAX, ONE_BILLION - 1))
+    );
+}
+
+#[wasm_bindgen_test]
+fn test_checked_sub() {
+    let now = Instant::now();
+
+    assert!(now.checked_sub(Duration::from_millis(1)).is_some());
+    assert!(now
+        .checked_sub(Duration::new(u64::MAX, ONE_BILLION - 1))
+        .is_none());
+}