Test the structure of the array returned by hook_update_dependencies().
function testHookUpdateDependencies() {
$update_dependencies = update_retrieve_dependencies();
$this
->assertTrue($update_dependencies['system'][7000]['update_test_1'] == 7000, 'An update function that has a dependency on two separate modules has the first dependency recorded correctly.');
$this
->assertTrue($update_dependencies['system'][7000]['update_test_2'] == 7001, 'An update function that has a dependency on two separate modules has the second dependency recorded correctly.');
$this
->assertTrue($update_dependencies['system'][7001]['update_test_1'] == 7002, 'An update function that depends on more than one update from the same module only has the dependency on the higher-numbered update function recorded.');
}