Use fentanyl test strips (a fentanyl test kit)
METHOD 1
If testing a benzo/opioid pill, crush one in a plastic baggie and dump out the powder.  Then add 10 drops of water into the baggie and mix well. Dip the test strip no higher than the thick line. Wait 15 seconds. Put the strip away and check in 5 minutes.
METHOD 2
Mix 100 mg of sample in 200 ml of water. Dip the test strip no higher than the thick line. Wait 15 seconds. Put the strip away and check in 5 minutes.
COMPARE RESULTS
1 line = fentanyl, 2 lines = no fentanyl. Faint lines also count. Ignore fentanyl tester results after 5 minutes.
To detect all ingredients and estimate their amount pair reagents with a TLC purity test kit.