Improve error thrown for invalid schema with multi source.

CHANGELOG.md

@@ -9,6 +9,7 @@
 - Speed up validating annotations with user fields ([#1078](../../pull/1078))
 - Speed up validating annotation colors ([#1080](../../pull/1080))
 - Support more complex bands from the test source ([#1082](../../pull/1082))
+- Improve error thrown for invalid schema with multi source ([#1083](../../pull/1083))
 
 ### Bug Fixes
 - The cache could reuse a class inappropriately ([#1070](../../pull/1070))

sources/multi/large_image_source_multi/__init__.py

@@ -423,7 +423,10 @@ def __init__(self, path, **kwargs):
                         self._info = yaml.safe_load(fptr)
             except (json.JSONDecodeError, yaml.YAMLError, UnicodeDecodeError):
                 raise TileSourceError('File cannot be opened via multi-source reader.')
-            self._validator.validate(self._info)
+            try:
+                self._validator.validate(self._info)
+            except jsonschema.ValidationError:
+                raise TileSourceError('File cannot be validated via multi-source reader.')
             self._basePath = Path(self._largeImagePath).parent
         self._basePath /= Path(self._info.get('basePath', '.'))
         for axis in self._info.get('axes', []):

test/test_source_multi.py

@@ -126,6 +126,15 @@ def testTilesFromMultiString():
         large_image_source_multi.open('invalid' + sourceString)
 
 
+def testTilesFromNonschemaMultiString():
+    sourceString = json.dumps({'sources': [{
+        'sourceName': 'test', 'path': '__none__',
+        'notAKnownKey': 'X',
+        'params': {'sizeX': 10000, 'sizeY': 10000}}]})
+    with pytest.raises(large_image.exceptions.TileSourceError):
+        large_image_source_multi.open(sourceString)
+
+
 @pytest.mark.skipif(sys.version_info < (3, 7), reason='requires python >= 3.7 for a sub-source')
 def testInternalMetadata(multiSourceImagePath):
     imagePath = multiSourceImagePath