def test_argument_collection():
arg = Argument('foo').retrieve('bar')
col = ArgumentCollection()
assert col.isempty()
col.add(arg)
assert not col.isempty()
assert col['foo'] == arg
col = ArgumentCollection.from_dict({'test': 'ing'})
assert col['test'].value == 'ing'
col1 = ArgumentCollection()
col2 = ArgumentCollection()
col1['foo'] = 'bar'
col2['foo'] = 'test'
assert col1.get('foo').value == 'bar'
assert col2.get('asdf') is None
col1.overwrite_merge(col2)
assert col1['foo'].value == 'test'
assert col.value('invalid') is None
assert col.value('test') == 'ing'
