Changes sk_path to sk_der in Watcher

The Watcher used to receive a secret key file path ion the __init__ to load a secret key for signing. That made testing the Watcher hard, since the file needed to be present. Changing it so the main (pisad) loads the file from disk and passes the data the Watcher on init.

test/unit/test_api.py

@@ -3,6 +3,7 @@ import pytest
 import requests
 from time import sleep
 from threading import Thread
+from cryptography.hazmat.primitives import serialization
 
 from pisa.api import start_api
 from pisa.watcher import Watcher
@@ -10,7 +11,13 @@ from pisa.tools import bitcoin_cli
 from pisa import HOST, PORT, c_logger
 from pisa.conf import MAX_APPOINTMENTS
 
-from test.unit.conftest import generate_block, generate_blocks, get_random_value_hex, generate_dummy_appointment_data
+from test.unit.conftest import (
+    generate_block,
+    generate_blocks,
+    get_random_value_hex,
+    generate_dummy_appointment_data,
+    generate_keypair,
+)
 
 from common.constants import LOCATOR_LEN_BYTES
 
@@ -25,7 +32,13 @@ locator_dispute_tx_map = {}
 
 @pytest.fixture(scope="module")
 def run_api(db_manager):
-    watcher = Watcher(db_manager)
+    sk, pk = generate_keypair()
+    sk_der = sk.private_bytes(
+        encoding=serialization.Encoding.DER,
+        format=serialization.PrivateFormat.TraditionalOpenSSL,
+        encryption_algorithm=serialization.NoEncryption(),
+    )
+    watcher = Watcher(db_manager, sk_der)
 
     api_thread = Thread(target=start_api, args=[watcher])
     api_thread.daemon = True