Add write example test

example.csv

@@ -0,0 +1,6 @@
+[section1]
+header1,header2,header3
+value1,value2,value3
+[section2]
+header4,header5,header6
+value4,value5,value6

tests/test_examples.py

@@ -1,6 +1,8 @@
 
 from pathlib import Path
 import pytest
+import io
+import csv
 
 import multicsv
 
@@ -39,3 +41,16 @@ def test_read_csv(example_file: Path) -> None:
 
         assert section1 == [['d', 'e', 'f'],
                             ['4', '5', '6']]
+
+
+def test_write_csv():
+    with multicsv.open('example.csv', mode='w+') as csv_file:
+        # Write the CSV content to the file
+        csv_file['section1'] = io.StringIO("header1,header2,header3\nvalue1,value2,value3\n")
+        csv_file['section2'] = io.StringIO("header4,header5,header6\nvalue4,value5,value6\n")
+
+        # Read a section using the csv module
+        section1 = csv_file['section1']
+        csv_reader = csv.reader(section1)
+        assert list(csv_reader) == [['header1', 'header2', 'header3'],
+                                    ['value1', 'value2', 'value3']]