test(core): tamper decoded ciphertext deterministically

sdk-core/src/test/java/com/xuqm/sdk/storage/AesGcmCodecTest.kt

@@ -4,6 +4,7 @@ import org.junit.Assert.assertEquals
 import org.junit.Assert.assertThrows
 import org.junit.Assert.assertTrue
 import org.junit.Test
+import java.util.Base64
 import javax.crypto.KeyGenerator
 
 class AesGcmCodecTest {
@@ -27,7 +28,11 @@ class AesGcmCodecTest {
         assertThrows(Exception::class.java) {
             AesGcmCodec.decrypt(key, encoded, "scope-b".toByteArray())
         }
-        val tampered = encoded.dropLast(1) + if (encoded.last() == 'A') "B" else "A"
+        val parts = encoded.split(".").toMutableList()
+        val cipherText = Base64.getUrlDecoder().decode(parts[2])
+        cipherText[cipherText.lastIndex] = (cipherText.last().toInt() xor 1).toByte()
+        parts[2] = Base64.getUrlEncoder().withoutPadding().encodeToString(cipherText)
+        val tampered = parts.joinToString(".")
         assertThrows(Exception::class.java) {
             AesGcmCodec.decrypt(key, tampered, "scope-a".toByteArray())
         }