function assertUserTables(schema, tableNames) {
  schema.tables().forEach(function(tableSchema) {
    assertTrue(tableNames.has(tableSchema.getName()));
  });
}
Asserts that an object store was created for each user-defined table.
@param {!lf.schema.Database} schema The database schema being tested.
@param {!lf.structs.Set<string>} tableNames The names of the tables that
    were created in the backing store.