diff --git a/actix-server/src/accept.rs b/actix-server/src/accept.rs
index 58f6c6be..571777b5 100644
--- a/actix-server/src/accept.rs
+++ b/actix-server/src/accept.rs
@@ -510,3 +510,63 @@ impl Accept {
         self.avail.set_available(idx, false);
     }
 }
+
+#[cfg(test)]
+mod test {
+    use super::Availability;
+
+    fn single(aval: &mut Availability, idx: usize) {
+        aval.set_available(idx, true);
+        assert!(aval.available());
+
+        aval.set_available(idx, false);
+        assert!(!aval.available());
+    }
+
+    fn multi(aval: &mut Availability, mut idx: Vec<usize>) {
+        idx.iter().for_each(|idx| aval.set_available(*idx, true));
+
+        assert!(aval.available());
+
+        while let Some(idx) = idx.pop() {
+            assert!(aval.available());
+            aval.set_available(idx, false);
+        }
+
+        assert!(!aval.available());
+    }
+
+    #[test]
+    fn availability() {
+        let mut aval = Availability::default();
+
+        single(&mut aval, 1);
+        single(&mut aval, 128);
+        single(&mut aval, 256);
+        single(&mut aval, 511);
+
+        let idx = (0..511).filter(|i| i % 3 == 0 && i % 5 == 0).collect();
+
+        multi(&mut aval, idx);
+
+        multi(&mut aval, (0..511).collect())
+    }
+
+    #[test]
+    #[should_panic]
+    fn overflow() {
+        let mut aval = Availability::default();
+        single(&mut aval, 512);
+    }
+
+    #[test]
+    fn pin_point() {
+        let mut aval = Availability::default();
+
+        aval.set_available(438, true);
+
+        aval.set_available(479, true);
+
+        assert_eq!(aval.0[3], 1 << (438 - 384) | 1 << (479 - 384));
+    }
+}