dash ble: add tests for StringLengthPrefixEncodingTest

We tested this part with a real pod and confirmed that it's working

omnipod-dash/src/test/java/info/nightscout/androidaps/plugins/pump/omnipod/dash/driver/comm/message/MessagePacketTest.kt

@@ -0,0 +1,5 @@
+package info.nightscout.androidaps.plugins.pump.omnipod.dash.driver.comm.message
+
+import org.junit.Assert.*
+
+class MessagePacketTest

omnipod-dash/src/test/java/info/nightscout/androidaps/plugins/pump/omnipod/dash/driver/comm/message/PayloadSplitJoinTest.kt

@@ -7,8 +7,8 @@ import org.junit.Test
 import java.util.*
 
 class PayloadSplitJoinTest {
+    private val random = Random(42)
 
-    val random = Random(42)
     @Test fun testSplitAndJoinBack() {
         for (s in 0..250) {
             val payload = ByteArray(s)

omnipod-dash/src/test/java/info/nightscout/androidaps/plugins/pump/omnipod/dash/driver/comm/message/StringLengthPrefixEncodingTest.kt

@@ -0,0 +1,22 @@
+package info.nightscout.androidaps.plugins.pump.omnipod.dash.driver.comm.message
+
+import com.google.crypto.tink.subtle.Hex
+import info.nightscout.androidaps.utils.extensions.toHex
+import org.junit.Assert.*
+import org.junit.Test
+
+class StringLengthPrefixEncodingTest {
+    private val p0Payload = Hex.decode("50,30,3d,00,01,a5".replace(",","")) // from logs
+    private val p0Content = Hex.decode("a5")
+
+    @Test fun testFormatKeysP0() {
+        val payload = StringLengthPrefixEncoding.formatKeys(arrayOf("P0="), arrayOf(p0Content))
+        assertEquals(p0Payload.toHex(), payload.toHex())
+    }
+
+    @Test fun testParseKeysP0() {
+        val parsed = StringLengthPrefixEncoding.parseKeys(arrayOf("P0="), p0Payload)
+        assertEquals(parsed.size, 1)
+        assertEquals(parsed[0].toHex(), p0Content.toHex())
+    }
+}