Added a test for the StringIO write() error I just fixed.
diff --git a/Lib/test/output/test_StringIO b/Lib/test/output/test_StringIO
index e2c5c31..e2b2893 100644
--- a/Lib/test/output/test_StringIO
+++ b/Lib/test/output/test_StringIO
@@ -3,6 +3,7 @@
 klmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ
 
 2
+'abcuvwxyz!'
 'abcdefghij'
 'abcde'
 Caught expected ValueError writing to closed StringIO:
@@ -11,6 +12,7 @@
 klmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ
 
 2
+'abcuvwxyz!'
 'abcdefghij'
 'abcde'
 Caught expected ValueError writing to closed StringIO:
diff --git a/Lib/test/test_StringIO.py b/Lib/test/test_StringIO.py
index b1fca84..ea237cd 100644
--- a/Lib/test/test_StringIO.py
+++ b/Lib/test/test_StringIO.py
@@ -8,6 +8,13 @@
     print len(f.readlines(60))
 
     f = module.StringIO()
+    f.write('abcdef')
+    f.seek(3)
+    f.write('uvwxyz')
+    f.write('!')
+    print `f.getvalue()`
+    f.close()
+    f = module.StringIO()
     f.write(s)
     f.seek(10)
     f.truncate()