diff -ru a/pyart/testing/data/make_small_mdv_ppi.py b/pyart/testing/data/make_small_mdv_ppi.py
--- a/pyart/testing/data/make_small_mdv_ppi.py	2022-07-19 13:06:08.000000000 -0500
+++ b/pyart/testing/data/make_small_mdv_ppi.py	2022-09-10 16:06:38.712279369 -0500
@@ -6,7 +6,10 @@
 """
 
 import struct
-import StringIO
+try:
+    from StringIO import StringIO
+except ImportError:
+    from io import StringIO
 import gzip
 
 import pyart
@@ -40,7 +43,7 @@
 
 fdata_str = fdata.astype('uint16').byteswap().tostring()
 uncompressed_data_size = len(fdata_str)
-fileobj = StringIO.StringIO()
+fileobj = StringIO()
 gzipfile = gzip.GzipFile(fileobj=fileobj, mode='w')
 gzipfile.write(fdata_str)
 gzipfile.close()
diff -ru a/pyart/testing/data/make_small_mdv_rhi.py b/pyart/testing/data/make_small_mdv_rhi.py
--- a/pyart/testing/data/make_small_mdv_rhi.py	2022-07-19 13:06:08.000000000 -0500
+++ b/pyart/testing/data/make_small_mdv_rhi.py	2022-09-10 16:07:12.775303046 -0500
@@ -6,7 +6,10 @@
 """
 
 import struct
-import StringIO
+try:
+    from StringIO import StringIO
+except ImportError:
+    from io import StringIO
 import gzip
 
 import pyart
@@ -39,7 +42,7 @@
 
 fdata_str = fdata.astype('uint16').byteswap().tostring()
 uncompressed_data_size = len(fdata_str)
-fileobj = StringIO.StringIO()
+fileobj = StringIO()
 gzipfile = gzip.GzipFile(fileobj=fileobj, mode='w')
 gzipfile.write(fdata_str)
 gzipfile.close()