TST: Use buffer instead of opening file many times

See py-pdf#2520, basically this was the last failing (only on windows) test
because if the pdfreaders are implicitly opening file streams that don't
get closed until they get garbage collected the .unlinks() create file
lock errors.

tests/test_writer.py

@@ -1118,7 +1118,7 @@ def test_append_multiple():
 
 
 @pytest.mark.samples()
-def test_set_page_label(pdf_file_path):
+def test_set_page_label():
     src = RESOURCE_ROOT / "GeoBase_NHNC1_Data_Model_UML_EN.pdf"  # File without labels
     reader = PdfReader(src)
 
@@ -1154,8 +1154,9 @@ def test_set_page_label(pdf_file_path):
     writer.set_page_label(11, 11, "/r")
     writer.set_page_label(12, 13, "/R")
     writer.set_page_label(17, 18, "/R")
-    writer.write(pdf_file_path)
-    assert PdfReader(pdf_file_path).page_labels == expected
+    _, buf = writer.write(BytesIO())
+    buf.seek(0)
+    assert PdfReader(buf).page_labels == expected
 
     writer = PdfWriter()  # Same labels, different set order
     writer.clone_document_from_reader(reader)
@@ -1165,8 +1166,9 @@ def test_set_page_label(pdf_file_path):
     writer.set_page_label(0, 1, "/r")
     writer.set_page_label(12, 13, "/R")
     writer.set_page_label(11, 11, "/r")
-    writer.write(pdf_file_path)
-    assert PdfReader(pdf_file_path).page_labels == expected
+    _, buf = writer.write(BytesIO())
+    buf.seek(0)
+    assert PdfReader(buf).page_labels == expected
 
     # Tests labels assigned only in the middle
     # Tests label assigned to a range already containing labled ranges
@@ -1176,8 +1178,9 @@ def test_set_page_label(pdf_file_path):
     writer.set_page_label(3, 4, "/a")
     writer.set_page_label(5, 5, "/A")
     writer.set_page_label(2, 6, "/r")
-    writer.write(pdf_file_path)
-    assert PdfReader(pdf_file_path).page_labels[: len(expected)] == expected
+    _, buf = writer.write(BytesIO())
+    buf.seek(0)
+    assert PdfReader(buf).page_labels[: len(expected)] == expected
 
     # Tests labels assigned inside a previously existing range
     expected = ["1", "2", "i", "a", "b", "A", "1", "1", "2"]
@@ -1187,8 +1190,9 @@ def test_set_page_label(pdf_file_path):
     writer.set_page_label(2, 6, "/r")
     writer.set_page_label(3, 4, "/a")
     writer.set_page_label(5, 5, "/A")
-    writer.write(pdf_file_path)
-    assert PdfReader(pdf_file_path).page_labels[: len(expected)] == expected
+    _, buf = writer.write(BytesIO())
+    buf.seek(0)
+    assert PdfReader(buf).page_labels[: len(expected)] == expected
 
     # Tests invalid user input
     writer = PdfWriter()
@@ -1212,7 +1216,6 @@ def test_set_page_label(pdf_file_path):
     ):
         writer.set_page_label(0, 5, "/r", start=-1)
 
-    pdf_file_path.unlink()
 
     src = (
         SAMPLE_ROOT / "009-pdflatex-geotopo/GeoTopo.pdf"
@@ -1224,18 +1227,18 @@ def test_set_page_label(pdf_file_path):
     writer = PdfWriter()
     writer.clone_document_from_reader(reader)
     writer.set_page_label(2, 3, "/A")
-    writer.write(pdf_file_path)
-    assert PdfReader(pdf_file_path).page_labels[: len(expected)] == expected
+    _, buf = writer.write(BytesIO())
+    buf.seek(0)
+    assert PdfReader(buf).page_labels[: len(expected)] == expected
 
     # Tests replacing existing lables
     expected = ["A", "B", "1", "1", "2"]
     writer = PdfWriter()
     writer.clone_document_from_reader(reader)
     writer.set_page_label(0, 1, "/A")
-    writer.write(pdf_file_path)
-    assert PdfReader(pdf_file_path).page_labels[: len(expected)] == expected
-
-    pdf_file_path.unlink()
+    _, buf = writer.write(BytesIO())
+    buf.seek(0)
+    assert PdfReader(buf).page_labels[: len(expected)] == expected
 
     # Tests prefix and start.
     src = RESOURCE_ROOT / "issue-604.pdf"  # File without page labels
@@ -1250,7 +1253,7 @@ def test_set_page_label(pdf_file_path):
     writer.set_page_label(11, 21, "/D", prefix="PAP-")
     writer.set_page_label(22, 30, "/D", prefix="FOLL-")
     writer.set_page_label(31, 39, "/D", prefix="HURT-")
-    writer.write(pdf_file_path)
+    writer.write(BytesIO())
 
 
 @pytest.mark.enable_socket()
@@ -1452,7 +1455,6 @@ def test_named_dest_page_number():
 
 
 def test_update_form_fields(tmp_path):
-    write_data_here = tmp_path / "out.pdf"
     writer = PdfWriter(clone_from=RESOURCE_ROOT / "FormTestFromOo.pdf")
     writer.update_page_form_field_values(
         writer.pages[0],
@@ -1476,8 +1478,8 @@ def test_update_form_fields(tmp_path):
         auto_regenerate=False,
     )
 
-    writer.write(write_data_here)
-    reader = PdfReader(write_data_here)
+    _, buf = writer.write(BytesIO())
+    reader = PdfReader(buf)
     flds = reader.get_fields()
     assert flds["CheckBox1"]["/V"] == "/Yes"
     assert flds["CheckBox1"].indirect_reference.get_object()["/AS"] == "/Yes"
@@ -1499,8 +1501,6 @@ def test_update_form_fields(tmp_path):
     assert all(x in flds["RadioGroup1"]["/_States_"] for x in ["/1", "/2", "/3"])
     assert all(x in flds["Liste1"]["/_States_"] for x in ["Liste1", "Liste2", "Liste3"])
 
-    Path(write_data_here).unlink()
-
 
 @pytest.mark.enable_socket()
 def test_iss1862():