The test data is generated as follows:

$ keytool -keystore keystore -genkey -alias mykey
The password for the keystore and the key is 123456.

The signer information is set as follows:

CN=Android, OU=Android, O=Android, L=Mountain View, ST=CA, C=US

Build a random apk (Bluetooth.apk is chosen arbitrary)

$ m Bluetooth
$ cp $ANDROID_PRODUCT_OUT/system/app/Bluetooth.apk ./test.apk

Sign it using the apksigner.

$ m apksigner
$ apksigner sign --ks keystore ./test.apk

Check that the idsig file is created.

$ ls -l test.apk*
-rw-r----- 1 jiyong primarygroup 3888734 Jun  4 01:08 test.apk
-rw-r----- 1 jiyong primarygroup   39115 Jun  4 01:08 test.apk.idsig