fix: expire client when elapsed time from trusted equals trusting period

.changelog/unreleased/bug-fixes/1239-consider-client-expired-at-trusting-period.md

@@ -0,0 +1,3 @@
+- [ibc-client-tendermint] Expire a client when the elapsed time from a trusted
+  header equals the trusting period, to stay consistent with the expiry logic in
+  `tendermint-rs` ([\#1239](https://github.com/cosmos/ibc-rs/issues/1239))

ibc-clients/ics07-tendermint/src/client_state/validation.rs

@@ -221,7 +221,10 @@ where
     if let Some(elapsed_since_latest_consensus_state) =
         now.duration_since(&latest_consensus_state.timestamp().into())
     {
-        if elapsed_since_latest_consensus_state > client_state.trusting_period {
+        // Note: The equality is considered as expired to stay consistent with
+        // the check in tendermint-rs, where a header at `trusted_header_time +
+        // trusting_period` is considered as expired.
+        if elapsed_since_latest_consensus_state >= client_state.trusting_period {
             return Ok(Status::Expired);
         }
     }

tests-integration/tests/core/ics02_client/update_client.rs

@@ -1431,7 +1431,7 @@ fn test_expired_client() {
         );
 
     while ctx.ibc_store.host_timestamp().expect("no error")
-        < (timestamp + trusting_period).expect("no error")
+        <= (timestamp + trusting_period).expect("no error")
     {
         ctx.advance_block_height();
     }