Adjust pinentry mock

The new test Docker image has a newer gnupg which does not behave the
same way, handling invalid passwords. This type of error is simulated
using an ICP error in the pinentry protocol.

test/pinentry-mock

@@ -1,12 +1,20 @@
 #!/bin/bash
 # This program is a custom mock pinentry program
-# It always uses whatever password is found in the /tmp directory
-password="$(cat /tmp/mock-password 2>/dev/null)"
+# It uses whatever password is found in the /tmp directory
+# If the password is empty, replies CANCEL causing an error to similate invalid
+# credentials
 echo "OK Pleased to meet you"
 while read -r line; do
   if [[ $line =~ GETPIN ]]; then
-    echo -n "D "
-    echo "$password"
+    password="$(cat /tmp/mock-password 2>/dev/null)"
+    if [ -n "$password" ]; then
+      echo -n "D "
+      echo "$password"
+      echo "OK";
+    else
+      echo "CANCEL";
+    fi
+  else
+    echo "OK";
   fi
-  echo "OK";
 done

test/test_encryption.py

@@ -214,7 +214,7 @@ def test_symmetric_encrypt(
     if missing_encrypt:
         assert 'does not exist' in run.err
     elif bad_phrase:
-        assert 'Invalid passphrase' in run.err
+        assert 'Invalid IPC' in run.err
     else:
         assert encrypted_data_valid(
             runner, gnupg, paths.archive, encrypt_targets)