require.NoError(t, err)

	allocated, length, err := m.allocateOne("one")
	assert.NoError(t, err)
	assert.Equal(t, userNsLength, int(length), "m.isSet(%d).length=%v", allocated, length)
	assert.Equal(t, true, m.isSet(allocated), "m.isSet(%d)", allocated)

	allocated2, length2, err := m.allocateOne("two")
	assert.NoError(t, err)
	assert.NotEqual(t, allocated, allocated2, "allocated != allocated2")

	if index < 0 || index >= m.len {
		return true
	}
	return m.used.Has(index)
}

// allocateOne finds a free user namespace and allocate it to the specified pod.
// The first return value is the first ID in the user namespace, the second returns
// the length for the user namespace range.
func (m *UsernsManager) allocateOne(pod types.UID) (firstID uint32, length uint32, err error) {
	firstZero, found, err := m.used.AllocateNext()