More information is needed regarding the children because CPS is looking to protect them. School absences or tardies, malnourishment, or other matters can indicate neglect and indicate drug use as reason for lack of involvement or neglect.
If CPS has a reasonable suspicion that you are using drugs and they ask you to drug test and you refuse - you will raise all kinds of red flags for them. They may start looking at you more critically and it could cause you more problems than it is worth to just swallow your righteous indignation and give them a drug test.
If you are not using drugs, the test will be negative and then you calmly explain that you would like them to take note of the person who made the complaint and not take that person so seriously next time.
Can they make you take a drug test?
Can they take your children away from you?
Please don't give them a reason to do that to your family.