[stdlib] Fix I/O related nodes (especially json), there were bad bugs with ioformat.

bonobo/util/testing.py

@@ -1,6 +1,7 @@
 from contextlib import contextmanager
 from unittest.mock import MagicMock
 
+from bonobo import open_fs
 from bonobo.execution.node import NodeExecutionContext
 
 
@@ -17,3 +18,20 @@ def optional_contextmanager(cm, *, ignore=False):
     else:
         with cm:
             yield
+
+
+class FilesystemTester:
+    def __init__(self, extension='txt', mode='w'):
+        self.extension = extension
+        self.input_data = ''
+        self.mode = mode
+
+    def get_services_for_reader(self, tmpdir):
+        fs, filename = open_fs(tmpdir), 'input.' + self.extension
+        with fs.open(filename, self.mode) as fp:
+            fp.write(self.input_data)
+        return fs, filename, {'fs': fs}
+
+    def get_services_for_writer(self, tmpdir):
+        fs, filename = open_fs(tmpdir), 'output.' + self.extension
+        return fs, filename, {'fs': fs}