py/stream: seek: Consistently handle negative offset for SEEK_SET.

Per POSIX, this is EINVAL, so raises OSError(EINVAL).

1 files changed, 13 insertions, 0 deletions

diff --git a/tests/io/bytesio_ext2.py b/tests/io/bytesio_ext2.py
new file mode 100644
index 000000000..c07ad900c
--- /dev/null
+++ b/tests/io/bytesio_ext2.py
@@ -0,0 +1,13 @@
+try:
+    import uio as io
+except ImportError:
+    import io
+
+a = io.BytesIO(b"foobar")
+try:
+    a.seek(-10)
+except Exception as e:
+    # CPython throws ValueError, but MicroPython has consistent stream
+    # interface, so BytesIO raises the same error as a real file, which
+    # is OSError(EINVAL).
+    print(repr(e))