Suppress some warnings during doctest

These are warnings that are normally suppressed, but unittest turns them
on. They're not helpful because it's complaining I'm not .close()ing
files, but adding that would make the documention less clear. So,
suppres them.

test-csppfetch.py

@@ -668,6 +668,21 @@ class DownloaderTests(DTestCase):
                 self.assertMockFile(outdir+"/avhrr-only-v2.20170105.nc")
 
 
+def add_module_doctest(tests, module, context):
+    import warnings
+    import doctest
+    def suppress(module):
+        for mod in (module, 'doctest'):
+            warnings.filterwarnings("ignore",
+                    message= r'unclosed file <_io.TextIOWrapper',
+                    category=ResourceWarning,
+                    module=mod+"$")
+    tests_before = tests.countTestCases()
+    tests.addTests(doctest.DocTestSuite(setUp=lambda x:suppress(module), globs=context))
+    tests_after = tests.countTestCases()
+    if tests_before >= tests_after:
+        raise Exception(f"Had {tests_before}, added doctests for {module.__name__}, then had {tests_after}, which is not more. Seems bad.")
+
 
 def load_tests(loader, tests, ignore):
     import doctest
@@ -712,25 +727,17 @@ def load_tests(loader, tests, ignore):
         'd': sst,
         }
 
-    print("start", tests.countTestCases())
-
     tests.addTests(doctest.DocTestSuite(globs=context))
-    print("self",tests.countTestCases())
 
-    tests.addTests(doctest.DocTestSuite(csppfetch, globs=context))
-    print("csppfetch", tests.countTestCases())
+    add_module_doctest(tests, csppfetch, context)
 
     import csppfetch.exclusivelockfile as exclusivelockfile
-    import csppfetch.daterange as daterange
-    tests.addTests(doctest.DocTestSuite(exclusivelockfile, globs=context))
-    print("exclusivelockfile", tests.countTestCases())
-
-    tests.addTests(doctest.DocTestSuite(daterange, globs=context))
-    print("daterange", tests.countTestCases())
+    add_module_doctest(tests, exclusivelockfile, context)
 
-    tests.addTests(doctest.DocTestSuite(csppfetch.timelimit, globs=context))
-    print("timelimit", tests.countTestCases())
+    import csppfetch.daterange as daterange
+    add_module_doctest(tests, daterange, context)
 
+    add_module_doctest(tests, csppfetch.timelimit, context)
 
     return tests