fix: implement closed property on fileio.py classes (#907)

* fix: implement closed property on fileio.py classes

* update tests

* fix numerous mistakes

google/cloud/storage/fileio.py

@@ -211,9 +211,9 @@ def seek(self, pos, whence=0):
     def close(self):
         self._buffer.close()
 
-    def _checkClosed(self):
-        if self._buffer.closed:
-            raise ValueError("I/O operation on closed file.")
+    @property
+    def closed(self):
+        return self._buffer.closed
 
     def readable(self):
         return True
@@ -431,9 +431,9 @@ def close(self):
             self._upload_chunks_from_buffer(1)
         self._buffer.close()
 
-    def _checkClosed(self):
-        if self._buffer.closed:
-            raise ValueError("I/O operation on closed file.")
+    @property
+    def closed(self):
+        return self._buffer.closed
 
     def readable(self):
         return False

tests/unit/test_fileio.py

@@ -287,6 +287,7 @@ def test_close(self):
         reader = self._make_blob_reader(blob)
 
         reader.close()
+        self.assertTrue(reader.closed)
 
         with self.assertRaises(ValueError):
             reader.read()
@@ -415,6 +416,8 @@ def test_close_errors(self):
         writer.close()
         # Close a second time to verify it successfully does nothing.
         writer.close()
+
+        self.assertTrue(writer.closed)
         # Try to write to closed file.
         with self.assertRaises(ValueError):
             writer.write(TEST_BINARY_DATA)
@@ -767,6 +770,7 @@ def test_seek(self):
     def test_close(self):
         buff = self._make_sliding_buffer()
         buff.close()
+        self.assertTrue(buff.closed)
         with self.assertRaises(ValueError):
             buff.read()
 
@@ -913,6 +917,7 @@ def test_close(self):
         reader = self._make_blob_reader(blob)
 
         reader.close()
+        self.assertTrue(reader.closed)
 
         with self.assertRaises(ValueError):
             reader.read()