fix(store): warn on init instead of throw

docker/credentials/store.py

@@ -2,6 +2,7 @@
 import json
 import shutil
 import subprocess
+import warnings
 
 from . import constants
 from . import errors
@@ -18,7 +19,7 @@ def __init__(self, program, environment=None):
         self.exe = shutil.which(self.program)
         self.environment = environment
         if self.exe is None:
-            raise errors.InitializationError(
+            warnings.warn(
                 '{} not installed or not available in PATH'.format(
                     self.program
                 )

tests/integration/credentials/store_test.py

@@ -84,3 +84,10 @@ def test_execute_with_env_override(self):
         data = self.store._execute('--null', '')
         assert b'\0FOO=bar\0' in data
         assert 'FOO' not in os.environ
+
+    def test_unavailable_store(self):
+        some_unavailable_store = None
+        with pytest.warns(UserWarning):
+            some_unavailable_store = Store('that-does-not-exist')
+        with pytest.raises(StoreError):
+            some_unavailable_store.get('anything-this-does-not-matter')