From d61bbc530f9326c3d7491f1a4e8ac195e4bee741 Mon Sep 17 00:00:00 2001
From: Jan Petykiewicz <jan@mpxd.net>
Date: Thu, 26 Jan 2023 13:48:20 -0800
Subject: [PATCH] Use IO[bytes] everywhere

---
 fatamorgana/test/build_testfiles.py        |  6 ++---
 fatamorgana/test/test_files_cblocks.py     |  6 ++---
 fatamorgana/test/test_files_cells.py       | 18 ++++++-------
 fatamorgana/test/test_files_circles.py     |  6 ++---
 fatamorgana/test/test_files_ctrapezoids.py |  8 +++---
 fatamorgana/test/test_files_empty.py       | 14 +++++-----
 fatamorgana/test/test_files_layernames.py  | 31 +++++++++++-----------
 fatamorgana/test/test_files_modals.py      |  6 ++---
 fatamorgana/test/test_files_paths.py       |  6 ++---
 fatamorgana/test/test_files_placements.py  | 21 ++++++++-------
 fatamorgana/test/test_files_polygons.py    |  8 +++---
 fatamorgana/test/test_files_properties.py  | 12 ++++-----
 fatamorgana/test/test_files_rectangles.py  |  6 ++---
 fatamorgana/test/test_files_texts.py       | 22 +++++++--------
 fatamorgana/test/test_files_trapezoids.py  |  6 ++---
 15 files changed, 88 insertions(+), 88 deletions(-)

diff --git a/fatamorgana/test/build_testfiles.py b/fatamorgana/test/build_testfiles.py
index e776c61..5bb7525 100644
--- a/fatamorgana/test/build_testfiles.py
+++ b/fatamorgana/test/build_testfiles.py
@@ -1,10 +1,8 @@
 '''
 Build files equivalent to the test cases used by KLayout.
 '''
-# type: ignore
 
-from typing import Callable
-from io import BufferedIOBase
+from typing import Callable, IO
 
 
 from . import (
@@ -16,7 +14,7 @@ from . import (
     )
 
 
-def build_file(num: str, func: Callable[[BufferedIOBase], BufferedIOBase]) -> None:
+def build_file(num: str, func: Callable[[IO[bytes]], IO[bytes]]) -> None:
     with open('t' + num + '.oas', 'wb') as f:
         func(f)
 
diff --git a/fatamorgana/test/test_files_cblocks.py b/fatamorgana/test/test_files_cblocks.py
index cf3f2ec..3f02e93 100644
--- a/fatamorgana/test/test_files_cblocks.py
+++ b/fatamorgana/test/test_files_cblocks.py
@@ -1,6 +1,6 @@
 # type: ignore
-
-from io import BytesIO, BufferedIOBase
+from typing import IO
+from io import BytesIO
 
 from numpy.testing import assert_equal
 
@@ -26,7 +26,7 @@ def base_tests(layout: OasisLayout) -> None:
     assert not layout.cells[0].properties
 
 
-def write_file_1(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_1(buf: IO[bytes]) -> IO[bytes]:
     '''
     '''
     buf.write(HEADER)
diff --git a/fatamorgana/test/test_files_cells.py b/fatamorgana/test/test_files_cells.py
index 9fae7b8..59bc6d4 100644
--- a/fatamorgana/test/test_files_cells.py
+++ b/fatamorgana/test/test_files_cells.py
@@ -1,6 +1,6 @@
 # type: ignore
-
-from io import BytesIO, BufferedIOBase
+from typing import IO
+from io import BytesIO
 
 import pytest
 
@@ -23,7 +23,7 @@ def base_tests(layout: OasisLayout) -> None:
     assert not layout.layers
 
 
-def write_file_1(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_1(buf: IO[bytes]) -> IO[bytes]:
     '''
     Single cell with explicit name 'XYZ'
     '''
@@ -48,7 +48,7 @@ def test_file_1() -> None:
     assert not layout.cellnames
 
 
-def write_file_2(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_2(buf: IO[bytes]) -> IO[bytes]:
     '''
     Two cellnames ('XYZ', 'ABC') and two cells with name references.
     '''
@@ -85,7 +85,7 @@ def test_file_2() -> None:
     assert layout.cells[1].name == 1
 
 
-def write_file_3(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_3(buf: IO[bytes]) -> IO[bytes]:
     '''
     Invalid file, contains a mix of explicit and implicit cellnames
     '''
@@ -116,7 +116,7 @@ def test_file_3() -> None:
         layout = OasisLayout.read(buf)
 
 
-def write_file_4(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_4(buf: IO[bytes]) -> IO[bytes]:
     '''
     Two cells referencing two names with explicit ids (unsorted)
     '''
@@ -155,7 +155,7 @@ def test_file_4() -> None:
     assert layout.cells[1].name == 1
 
 
-def write_file_5(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_5(buf: IO[bytes]) -> IO[bytes]:
     '''
     Reference to non-existent cell name.
     '''
@@ -196,7 +196,7 @@ def test_file_5() -> None:
     #TODO add optional error checking for this case
 
 
-def write_file_6(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_6(buf: IO[bytes]) -> IO[bytes]:
     '''
     Cellname with invalid n-string.
     '''
@@ -237,7 +237,7 @@ def test_file_6() -> None:
     #assert layout.cells[1].name == 1
 
 
-def write_file_7(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_7(buf: IO[bytes]) -> IO[bytes]:
     '''
     Unused cellname.
     '''
diff --git a/fatamorgana/test/test_files_circles.py b/fatamorgana/test/test_files_circles.py
index 794c18f..f29b18f 100644
--- a/fatamorgana/test/test_files_circles.py
+++ b/fatamorgana/test/test_files_circles.py
@@ -1,6 +1,6 @@
 # type: ignore
-
-from io import BytesIO, BufferedIOBase
+from typing import IO
+from io import BytesIO
 
 from .utils import HEADER, FOOTER
 from ..basic import write_uint, write_sint, write_bstring, write_byte
@@ -24,7 +24,7 @@ def base_tests(layout: OasisLayout) -> None:
     assert not layout.cells[0].properties
 
 
-def write_file_1(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_1(buf: IO[bytes]) -> IO[bytes]:
     '''
     '''
     buf.write(HEADER)
diff --git a/fatamorgana/test/test_files_ctrapezoids.py b/fatamorgana/test/test_files_ctrapezoids.py
index fdcc6cf..095909f 100644
--- a/fatamorgana/test/test_files_ctrapezoids.py
+++ b/fatamorgana/test/test_files_ctrapezoids.py
@@ -1,6 +1,6 @@
 # type: ignore
-
-from io import BytesIO, BufferedIOBase
+from typing import IO
+from io import BytesIO
 
 from .utils import HEADER, FOOTER
 from ..basic import write_uint, write_sint, write_bstring, write_byte
@@ -20,7 +20,7 @@ def base_tests(layout: OasisLayout) -> None:
     assert not layout.layers
 
 
-def write_file_1(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_1(buf: IO[bytes]) -> IO[bytes]:
     '''
     '''
     buf.write(HEADER)
@@ -153,7 +153,7 @@ def test_file_1() -> None:
     assert geometry[55].repetition.b_vector == [0, 300]
 
 
-def write_file_2(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_2(buf: IO[bytes]) -> IO[bytes]:
     '''
     '''
     buf.write(HEADER)
diff --git a/fatamorgana/test/test_files_empty.py b/fatamorgana/test/test_files_empty.py
index acf651d..8554c28 100644
--- a/fatamorgana/test/test_files_empty.py
+++ b/fatamorgana/test/test_files_empty.py
@@ -1,6 +1,6 @@
 # type: ignore
-
-from io import BytesIO, BufferedIOBase
+from typing import IO
+from io import BytesIO
 import struct
 
 from .utils import MAGIC_BYTES, FOOTER
@@ -22,7 +22,7 @@ def base_tests(layout: OasisLayout) -> None:
     assert not layout.layers
 
 
-def write_file_1(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_1(buf: IO[bytes]) -> IO[bytes]:
     '''
     File contains one PAD record.
     1000 units/micron
@@ -55,7 +55,7 @@ def test_file_1() -> None:
     assert layout.unit == 1000
 
 
-def write_file_2(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_2(buf: IO[bytes]) -> IO[bytes]:
     '''
     File contains no records.
     1/2 unit/micron
@@ -86,7 +86,7 @@ def test_file_2() -> None:
     assert layout.unit == 0.5
 
 
-def write_file_3(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_3(buf: IO[bytes]) -> IO[bytes]:
     '''
     File contains no records.
     10/4 unit/micron
@@ -118,7 +118,7 @@ def test_file_3() -> None:
     assert layout.unit == 10 / 4
 
 
-def write_file_4(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_4(buf: IO[bytes]) -> IO[bytes]:
     '''
     File contains no records.
     12.5 unit/micron (float32)
@@ -149,7 +149,7 @@ def test_file_4() -> None:
     assert layout.unit == 12.5
 
 
-def write_file_5(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_5(buf: IO[bytes]) -> IO[bytes]:
     '''
     File contains no records.
     12.5 unit/micron (float64)
diff --git a/fatamorgana/test/test_files_layernames.py b/fatamorgana/test/test_files_layernames.py
index 94a2cc8..d430aaf 100644
--- a/fatamorgana/test/test_files_layernames.py
+++ b/fatamorgana/test/test_files_layernames.py
@@ -1,18 +1,19 @@
 # type: ignore
-from typing import Sequence
+from typing import Sequence, IO
 
-from io import BytesIO, BufferedIOBase
+from io import BytesIO
 
 from .utils import HEADER, FOOTER
 from ..basic import write_uint, write_sint, write_bstring, write_byte
 from ..main import OasisLayout
 
 
-LAYERS = [(1, 2), (1, 5), (1, 6), (1, 8),
-          (5, 2), (5, 5), (5, 6), (5, 8),
-          (6, 2), (6, 5), (6, 6), (6, 8),
-          (7, 2), (7, 5), (7, 6), (7, 8),
-          ]
+LAYERS = [
+    (1, 2), (1, 5), (1, 6), (1, 8),
+    (5, 2), (5, 5), (5, 6), (5, 8),
+    (6, 2), (6, 5), (6, 6), (6, 8),
+    (7, 2), (7, 5), (7, 6), (7, 8),
+    ]
 
 def base_tests(layout: OasisLayout) -> None:
     assert layout.version.string == '1.0'
@@ -30,7 +31,7 @@ def base_tests(layout: OasisLayout) -> None:
     assert not layout.cells[0].properties
 
 
-def write_names_geom(buf: BufferedIOBase, short: bool = False) -> BufferedIOBase:
+def write_names_geom(buf: IO[bytes], short: bool = False) -> IO[bytes]:
     write_uint(buf, 11)           # LAYERNAME record (geometry)
     write_bstring(buf, b'AA')     # name
     write_uint(buf, 0)            # all layers
@@ -96,7 +97,7 @@ def write_names_geom(buf: BufferedIOBase, short: bool = False) -> BufferedIOBase
     return buf
 
 
-def write_names_text(buf: BufferedIOBase, prefix: bytes = b'') -> BufferedIOBase:
+def write_names_text(buf: IO[bytes], prefix: bytes = b'') -> IO[bytes]:
     write_uint(buf, 12)         # LAYERNAME record (geometry)
     write_bstring(buf, prefix + b'AA')   # name
     write_uint(buf, 0)          # all layers
@@ -128,7 +129,7 @@ def write_names_text(buf: BufferedIOBase, prefix: bytes = b'') -> BufferedIOBase
     write_uint(buf, 0)          # all datatypes
     return buf
 
-def write_geom(buf: BufferedIOBase) -> BufferedIOBase:
+def write_geom(buf: IO[bytes]) -> IO[bytes]:
     for ll, dt in LAYERS:
         write_uint(buf, 27)           # CIRCLE record
         write_byte(buf, 0b0011_1011)  # 00rX_YRDL
@@ -140,7 +141,7 @@ def write_geom(buf: BufferedIOBase) -> BufferedIOBase:
     return buf
 
 
-def write_text(buf: BufferedIOBase) -> BufferedIOBase:
+def write_text(buf: IO[bytes]) -> IO[bytes]:
     for ll, dt in LAYERS:
         write_uint(buf, 19)              # TEXT record
         write_byte(buf, 0b0101_1011)     # 0CNX_YRTL
@@ -205,7 +206,7 @@ def elem_test_text(geometry: Sequence) -> None:
         assert not gg.properties, msg
 
 
-def write_file_1(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_1(buf: IO[bytes]) -> IO[bytes]:
     '''
     '''
     buf.write(HEADER)
@@ -235,7 +236,7 @@ def test_file_1() -> None:
     name_test(layout.layers, is_textlayer=False)
 
 
-def write_file_2(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_2(buf: IO[bytes]) -> IO[bytes]:
     '''
     '''
     buf.write(HEADER)
@@ -265,7 +266,7 @@ def test_file_2() -> None:
     name_test(layout.layers, is_textlayer=True)
 
 
-def write_file_3(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_3(buf: IO[bytes]) -> IO[bytes]:
     '''
     '''
     buf.write(HEADER)
@@ -281,7 +282,7 @@ def write_file_3(buf: BufferedIOBase) -> BufferedIOBase:
     return buf
 
 
-def write_file_4(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_4(buf: IO[bytes]) -> IO[bytes]:
     '''
     '''
     buf.write(HEADER)
diff --git a/fatamorgana/test/test_files_modals.py b/fatamorgana/test/test_files_modals.py
index d2417f2..9eac770 100644
--- a/fatamorgana/test/test_files_modals.py
+++ b/fatamorgana/test/test_files_modals.py
@@ -1,6 +1,6 @@
 # type: ignore
-
-from io import BytesIO, BufferedIOBase
+from typing import IO
+from io import BytesIO
 
 from .utils import HEADER, FOOTER
 from ..basic import write_uint, write_sint, write_bstring, write_byte
@@ -20,7 +20,7 @@ def base_tests(layout: OasisLayout) -> None:
     assert not layout.layers
 
 
-def write_file_1(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_1(buf: IO[bytes]) -> IO[bytes]:
     '''
     '''
     buf.write(HEADER)
diff --git a/fatamorgana/test/test_files_paths.py b/fatamorgana/test/test_files_paths.py
index 8fb2cc0..3243a79 100644
--- a/fatamorgana/test/test_files_paths.py
+++ b/fatamorgana/test/test_files_paths.py
@@ -1,6 +1,6 @@
 # type: ignore
-
-from io import BytesIO, BufferedIOBase
+from typing import IO
+from io import BytesIO
 
 from numpy.testing import assert_equal
 
@@ -26,7 +26,7 @@ def base_tests(layout: OasisLayout) -> None:
     assert not layout.cells[0].properties
 
 
-def write_file_1(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_1(buf: IO[bytes]) -> IO[bytes]:
     '''
     '''
     buf.write(HEADER)
diff --git a/fatamorgana/test/test_files_placements.py b/fatamorgana/test/test_files_placements.py
index 390876e..290ffee 100644
--- a/fatamorgana/test/test_files_placements.py
+++ b/fatamorgana/test/test_files_placements.py
@@ -1,11 +1,12 @@
 # type: ignore
-from typing import Tuple
-from io import BytesIO, BufferedIOBase
+from typing import Tuple, IO, cast, List
+from io import BytesIO
 
 from numpy.testing import assert_equal
 
 from .utils import HEADER, FOOTER
 from ..basic import write_uint, write_sint, write_bstring, write_byte, write_float32, write_float64
+from ..records import Rectangle
 from ..main import OasisLayout
 
 
@@ -21,7 +22,7 @@ def base_tests(layout: OasisLayout) -> None:
     assert not layout.layers
 
 
-def write_rectangle(buf: BufferedIOBase, pos: Tuple[int, int] = (300, -400)) -> None:
+def write_rectangle(buf: IO[bytes], pos: Tuple[int, int] = (300, -400)) -> None:
     write_uint(buf, 20)           # RECTANGLE record
     write_byte(buf, 0b0111_1011)  # SWHX_YRDL
     write_uint(buf, 1)            # layer
@@ -32,7 +33,7 @@ def write_rectangle(buf: BufferedIOBase, pos: Tuple[int, int] = (300, -400)) ->
     write_sint(buf, pos[1])       # geometry-y (absolute)
 
 
-def write_file_1(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_1(buf: IO[bytes]) -> IO[bytes]:
     '''
     '''
     buf.write(HEADER)
@@ -173,7 +174,7 @@ def test_file_1() -> None:
     assert not layout.cells[1].properties
     assert not layout.cells[1].geometry
 
-    geometry = layout.cells[0].geometry
+    geometry = cast(List[Rectangle], layout.cells[0].geometry)
     assert len(geometry) == 1
     assert geometry[0].layer == 1
     assert geometry[0].datatype == 2
@@ -248,7 +249,7 @@ def test_file_1() -> None:
     assert placements[12].repetition.b_vector == [-330, 330]
 
 
-def write_file_common(buf: BufferedIOBase, variant: int) -> BufferedIOBase:
+def write_file_common(buf: IO[bytes], variant: int) -> IO[bytes]:
     '''
     '''
     assert variant in (2, 3, 5, 7), 'Error in test definition!'
@@ -514,7 +515,7 @@ def common_tests(layout: OasisLayout, variant: int) -> None:
     assert placements[6].y == 2400
 
 
-def write_file_4(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_4(buf: IO[bytes]) -> IO[bytes]:
     '''
     '''
     buf.write(HEADER)
@@ -593,7 +594,7 @@ def write_file_4(buf: BufferedIOBase) -> BufferedIOBase:
     return buf
 
 
-def write_file_6(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_6(buf: IO[bytes]) -> IO[bytes]:
     '''
     '''
     buf.write(HEADER)
@@ -746,7 +747,7 @@ def test_file_6() -> None:
         assert pp.y == [0, 1000][ii], msg
 
 
-def write_file_8(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_8(buf: IO[bytes]) -> IO[bytes]:
     '''
     '''
     buf.write(HEADER)
@@ -842,7 +843,7 @@ def test_file_8() -> None:
     assert not layout.cells[2].properties
     assert not layout.cells[2].placements
 
-    geometry = layout.cells[2].geometry
+    geometry = cast(List[Rectangle], layout.cells[2].geometry)
     assert len(geometry) == 1
     assert geometry[0].layer == 1
     assert geometry[0].datatype == 2
diff --git a/fatamorgana/test/test_files_polygons.py b/fatamorgana/test/test_files_polygons.py
index 2deb808..f89a019 100644
--- a/fatamorgana/test/test_files_polygons.py
+++ b/fatamorgana/test/test_files_polygons.py
@@ -1,6 +1,6 @@
 # type: ignore
-
-from io import BytesIO, BufferedIOBase
+from typing import IO
+from io import BytesIO
 
 import numpy
 from numpy.testing import assert_equal
@@ -106,7 +106,7 @@ def common_tests(layout: OasisLayout) -> None:
         assert_equal(geometry[ii].point_list, [[0, 150], [50, 0], [0, -50], [50, 0], [0, -100], [-100, 0]], err_msg=msg)
 
 
-def write_file_common(buf: BufferedIOBase, variant: int) -> BufferedIOBase:
+def write_file_common(buf: IO[bytes], variant: int) -> IO[bytes]:
     '''
     '''
     assert variant in (1, 3), 'Error in test!!'
@@ -375,7 +375,7 @@ def test_file_1() -> None:
         assert not gg.properties, f'Fail on polygon {ii}'
 
 
-def write_file_2(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_2(buf: IO[bytes]) -> IO[bytes]:
     '''
     '''
     buf.write(HEADER)
diff --git a/fatamorgana/test/test_files_properties.py b/fatamorgana/test/test_files_properties.py
index 107b64a..99bdc37 100644
--- a/fatamorgana/test/test_files_properties.py
+++ b/fatamorgana/test/test_files_properties.py
@@ -1,6 +1,6 @@
 # type: ignore
-
-from io import BytesIO, BufferedIOBase
+from typing import IO
+from io import BytesIO
 
 import pytest
 from numpy.testing import assert_equal
@@ -23,7 +23,7 @@ def base_tests(layout: OasisLayout) -> None:
     assert not layout.layers
 
 
-def write_file_common(buf: BufferedIOBase, variant: int) -> BufferedIOBase:
+def write_file_common(buf: IO[bytes], variant: int) -> IO[bytes]:
     '''
     '''
     include_repetitions = variant in (2, 5)
@@ -354,7 +354,7 @@ def test_file_5() -> None:
         assert gg.repetition.b_vector == [0, 320], msg
 
 
-def write_file_3(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_3(buf: IO[bytes]) -> IO[bytes]:
     '''
     '''
     buf.write(HEADER)
@@ -579,7 +579,7 @@ def test_file_3() -> None:
         assert geometry[ii].properties[0].values[1].string == 'PROP_VALUE2', msg
 
 
-def write_file_4_6(buf: BufferedIOBase, variant: int) -> BufferedIOBase:
+def write_file_4_6(buf: IO[bytes], variant: int) -> IO[bytes]:
     '''
     '''
     buf.write(HEADER)
@@ -927,7 +927,7 @@ def test_file_6() -> None:
         assert placements[ii].properties[0].values[1].string == 'PROP_VALUE2', msg
 
 
-def write_file_7_8_9(buf: BufferedIOBase, variant: int) -> BufferedIOBase:
+def write_file_7_8_9(buf: IO[bytes], variant: int) -> IO[bytes]:
     '''
     '''
     buf.write(HEADER)
diff --git a/fatamorgana/test/test_files_rectangles.py b/fatamorgana/test/test_files_rectangles.py
index e9f0b99..a7ffdc7 100644
--- a/fatamorgana/test/test_files_rectangles.py
+++ b/fatamorgana/test/test_files_rectangles.py
@@ -1,6 +1,6 @@
 # type: ignore
-
-from io import BytesIO, BufferedIOBase
+from typing import IO
+from io import BytesIO
 
 from .utils import HEADER, FOOTER
 from ..basic import write_uint, write_sint, write_bstring, write_byte
@@ -74,7 +74,7 @@ def base_tests(layout: OasisLayout) -> None:
     assert geometry[10].repetition.x_displacements == [200, 300]
 
 
-def write_file_common(buf: BufferedIOBase, variant: int) -> BufferedIOBase:
+def write_file_common(buf: IO[bytes], variant: int) -> IO[bytes]:
     '''
     '''
     assert variant in (1, 2), 'Error in test!!'
diff --git a/fatamorgana/test/test_files_texts.py b/fatamorgana/test/test_files_texts.py
index 0ee22a0..0d10744 100644
--- a/fatamorgana/test/test_files_texts.py
+++ b/fatamorgana/test/test_files_texts.py
@@ -1,6 +1,6 @@
 # type: ignore
-
-from io import BytesIO, BufferedIOBase
+from typing import IO
+from io import BytesIO
 
 import pytest
 
@@ -99,7 +99,7 @@ def common_tests(layout: OasisLayout) -> None:
     assert geometry[19].repetition.y_displacements == [12, -9]
 
 
-def write_file_common(buf: BufferedIOBase, variant: int) -> BufferedIOBase:
+def write_file_common(buf: IO[bytes], variant: int) -> IO[bytes]:
     '''
     Single cell with explicit name 'XYZ'
     '''
@@ -460,7 +460,7 @@ def test_file_12() -> None:
     assert layout.textstrings[2].string == 'B'
 
 
-def write_file_3(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_3(buf: IO[bytes]) -> IO[bytes]:
     '''
     File with one textstring with explicit id, and one with an implicit id.
     Should fail.
@@ -497,7 +497,7 @@ def test_file_3() -> None:
         layout = OasisLayout.read(buf)
 
 
-def write_file_4(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_4(buf: IO[bytes]) -> IO[bytes]:
     '''
     File with a TEXT record that references a non-existent TEXTSTRING
 
@@ -537,7 +537,7 @@ def test_file_4() -> None:
     base_tests(layout)
 
 
-def write_file_6(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_6(buf: IO[bytes]) -> IO[bytes]:
     '''
     File with TEXT record that uses an un-filled modal for the repetition
     '''
@@ -570,7 +570,7 @@ def test_file_6() -> None:
         layout = OasisLayout.read(buf)
 
 
-def write_file_7(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_7(buf: IO[bytes]) -> IO[bytes]:
     '''
     File with TEXT record that uses an un-filled modal for the layer
     '''
@@ -601,7 +601,7 @@ def test_file_7() -> None:
         layout = OasisLayout.read(buf)
 
 
-def write_file_8(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_8(buf: IO[bytes]) -> IO[bytes]:
     '''
     File with TEXT record that uses an un-filled modal for the datatype
     '''
@@ -632,7 +632,7 @@ def test_file_8() -> None:
         layout = OasisLayout.read(buf)
 
 
-def write_file_9(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_9(buf: IO[bytes]) -> IO[bytes]:
     '''
     File with TEXT record that uses a default modal for the x coordinate
     '''
@@ -668,7 +668,7 @@ def test_file_9() -> None:
     assert text.y == -200
 
 
-def write_file_10(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_10(buf: IO[bytes]) -> IO[bytes]:
     '''
     File with TEXT record that uses a default modal for the y coordinate
     '''
@@ -704,7 +704,7 @@ def test_file_10() -> None:
     assert text.x == 100
 
 
-def write_file_11(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_11(buf: IO[bytes]) -> IO[bytes]:
     '''
     File with TEXT record that uses an un-filled modal for the text string
     '''
diff --git a/fatamorgana/test/test_files_trapezoids.py b/fatamorgana/test/test_files_trapezoids.py
index 574054d..cea3123 100644
--- a/fatamorgana/test/test_files_trapezoids.py
+++ b/fatamorgana/test/test_files_trapezoids.py
@@ -1,6 +1,6 @@
 # type: ignore
-
-from io import BytesIO, BufferedIOBase
+from typing import IO
+from io import BytesIO
 
 from .utils import HEADER, FOOTER
 from ..basic import write_uint, write_sint, write_bstring, write_byte
@@ -24,7 +24,7 @@ def base_tests(layout: OasisLayout) -> None:
     assert not layout.cells[0].properties
 
 
-def write_file_1(buf: BufferedIOBase) -> BufferedIOBase:
+def write_file_1(buf: IO[bytes]) -> IO[bytes]:
     '''
     '''
     buf.write(HEADER)