mvcc: test racey Hash call to backend panic

mvcc/kvstore_test.go

@@ -515,6 +515,20 @@ func TestTxnBlockBackendForceCommit(t *testing.T) {
 	}
 }
 
+// TestStoreHashAfterForceCommit ensures that later Hash call to
+// closed backend with ForceCommit does not panic.
+func TestStoreHashAfterForceCommit(t *testing.T) {
+	be, tmpPath := backend.NewDefaultTmpBackend()
+	kv := NewStore(be, &lease.FakeLessor{}, nil)
+	defer os.Remove(tmpPath)
+
+	// as in EtcdServer.HardStop
+	kv.Close()
+	be.Close()
+
+	kv.Hash()
+}
+
 // TODO: test attach key to lessor
 
 func newTestRevBytes(rev revision) []byte {