@Test
  public void testNamespaceExists() {
    Namespace namespace = Namespace.of("dbname_exists");

    catalog.createNamespace(namespace, meta);

    assertThat(catalog.namespaceExists(namespace)).as("Should true to namespace exist").isTrue();
    assertThat(catalog.namespaceExists(Namespace.of("db2", "db2", "ns2")))
        .as("Should false to namespace doesn't exist")
        .isFalse();
  }
Run all the tests from abstract of {@link CatalogTests} with few specific tests related to HIVE.
iceberg/iceberg-catalog/src/test/java/org/apache/iceberg/hive/TestHiveCatalog.java