From a4c4c72174a8a0fc710417eeeb13566b1723ac87 Mon Sep 17 00:00:00 2001
From: Jack Grigg <jack@electriccoin.co>
Date: Wed, 6 Dec 2023 08:57:16 +0000
Subject: [PATCH] Test `DiversifierIndex::increment`

Closes zcash/zip32#8.
---
 src/lib.rs | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/src/lib.rs b/src/lib.rs
index fd42eb6..18f8825 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -326,4 +326,33 @@ mod tests {
 
         assert!(DiversifierIndex::try_from(0x0100_0000_0000_0000_0000_0000_u128).is_err());
     }
+
+    #[test]
+    fn diversifier_index_increment() {
+        let mut di = DiversifierIndex::new();
+        assert_eq!(di, 0_u32.into());
+
+        assert_matches!(di.increment(), Ok(_));
+        assert_eq!(di, 1_u32.into());
+
+        assert_matches!(di.increment(), Ok(_));
+        assert_eq!(di, 2_u32.into());
+
+        let mut di = DiversifierIndex::from(0xff_u32);
+        assert_eq!(di, 0x00ff_u32.into());
+
+        assert_matches!(di.increment(), Ok(_));
+        assert_eq!(di, 0x0100_u32.into());
+
+        assert_matches!(di.increment(), Ok(_));
+        assert_eq!(di, 0x0101_u32.into());
+
+        let mut di = DiversifierIndex::try_from(0x00ff_ffff_ffff_ffff_ffff_fffe_u128).unwrap();
+        assert_eq!(u128::from(di), 0x00ff_ffff_ffff_ffff_ffff_fffe_u128);
+
+        assert_matches!(di.increment(), Ok(_));
+        assert_eq!(u128::from(di), 0x00ff_ffff_ffff_ffff_ffff_ffff_u128);
+
+        assert_matches!(di.increment(), Err(_));
+    }
 }