Mock PackageInfo.signatures by SHA1 fingerprint string

I've implemented the validation for incompatible app in my android application by comparing package name and signature of PackageInfo. I get information about installed packages by:

val packages = context.ctx.packageManager.getInstalledPackages(PackageManager.GET_META_DATA or PackageManager.GET_SIGNATURES)

and after that just compare strings of package names and signatures. I convert PackageInfo.signatures into Hex by this function:

fun bytesToHex(bytes: ByteArray): String {
        val hexArray = charArrayOf('0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F')
        val hexChars = CharArray(bytes.size * 2)
        var v: Int
        for (j in bytes.indices) {
            v = bytes[j].toInt() and 0xFF
            hexChars[j * 2] = hexArray[v.ushr(4)]
            hexChars[j * 2 + 1] = hexArray[v and 0x0F]
        }
        return String(hexChars)
}

and it works fine.

Now I want to implement several unit tests for this functionality and faced difficulties: how can I mock PackageInfo.signatures? How can I translate my SHA1 fingerprint string into android.content.pm.Signature?