diff --git a/tests/test_download.py b/tests/test_download.py
index 9a041088..5cf07af8 100755
--- a/tests/test_download.py
+++ b/tests/test_download.py
@@ -290,6 +290,9 @@ def test_https_connection(self):
       # Trust the certfile that happens to use a different hostname than we
       # will expect.
       os.environ['REQUESTS_CA_BUNDLE'] = bad_cert_fname
+      # Clear sessions to ensure that the certificate we just specified is used.
+      # TODO: Confirm necessity of this session clearing and lay out mechanics.
+      tuf.download._sessions = {}
 
       # Try connecting to the server process with the bad cert while trusting
       # the bad cert. Expect failure because even though we trust it, the
@@ -316,8 +319,12 @@ def test_https_connection(self):
       with self.assertRaises(requests.exceptions.SSLError):
         download.unsafe_download(good2_https_url, target_data_length)
 
+
       # Configure environment to now trust the certfile that is expired.
       os.environ['REQUESTS_CA_BUNDLE'] = expired_cert_fname
+      # Clear sessions to ensure that the certificate we just specified is used.
+      # TODO: Confirm necessity of this session clearing and lay out mechanics.
+      tuf.download._sessions = {}
 
       # Try connecting to the server process with the expired cert while
       # trusting the expired cert. Expect failure because even though we trust
@@ -328,20 +335,23 @@ def test_https_connection(self):
       with self.assertRaises(requests.exceptions.SSLError):
         download.unsafe_download(expired_https_url, target_data_length)
 
+
       # Try connecting to the server processes with the good certs while
       # trusting the appropriate good certs. Expect success.
-      # Note: running these OK downloads at the top of this try section causes
-      #       a failure in a previous assertion: retrieving the same good URL
-      #       again after no longer "trusting" the good certfile still succeeds
-      #       if we had previously succeeded in retrieving that same URL while
-      #       still trusting the good cert. Perhaps it's a caching issue....?
-      #       I'm not especially concerned yet, but take note for later....
+      # TODO: expand testing to switch expected certificates back and forth a
+      #       bit more while clearing / not clearing sessions.
       os.environ['REQUESTS_CA_BUNDLE'] = good_cert_fname
+      # Clear sessions to ensure that the certificate we just specified is used.
+      # TODO: Confirm necessity of this session clearing and lay out mechanics.
+      tuf.download._sessions = {}
       logger.info('Trying HTTPS download of target file: ' + good_https_url)
       download.safe_download(good_https_url, target_data_length)
       download.unsafe_download(good_https_url, target_data_length)
 
       os.environ['REQUESTS_CA_BUNDLE'] = good2_cert_fname
+      # Clear sessions to ensure that the certificate we just specified is used.
+      # TODO: Confirm necessity of this session clearing and lay out mechanics.
+      tuf.download._sessions = {}
       logger.info('Trying HTTPS download of target file: ' + good2_https_url)
       download.safe_download(good2_https_url, target_data_length)
       download.unsafe_download(good2_https_url, target_data_length)
diff --git a/tests/test_proxy_use.py b/tests/test_proxy_use.py
index bed8ea43..90832ae7 100644
--- a/tests/test_proxy_use.py
+++ b/tests/test_proxy_use.py
@@ -238,6 +238,9 @@ def test_https_dl_via_smart_http_proxy(self):
 
     self.set_env_value('REQUESTS_CA_BUNDLE',
         os.path.join('ssl_certs', 'ssl_cert.crt'))
+    # Clear sessions to ensure that the certificate we just specified is used.
+    # TODO: Confirm necessity of this session clearing and lay out mechanics.
+    tuf.download._sessions = {}
 
     logger.info('Trying HTTPS download via HTTP proxy: ' + self.url_https)
     download.safe_download(self.url_https, self.target_data_length)
@@ -259,6 +262,9 @@ def test_http_dl_via_https_proxy(self):
     # plain HTTP connection to the target server.
     self.set_env_value('REQUESTS_CA_BUNDLE',
         os.path.join('ssl_certs', 'proxy_ca.crt'))
+    # Clear sessions to ensure that the certificate we just specified is used.
+    # TODO: Confirm necessity of this session clearing and lay out mechanics.
+    tuf.download._sessions = {}
 
     logger.info('Trying HTTP download via HTTPS proxy: ' + self.url_https)
     download.safe_download(self.url, self.target_data_length)
@@ -282,6 +288,9 @@ def test_https_dl_via_https_proxy(self):
     # started in setUpClass().
     self.set_env_value('REQUESTS_CA_BUNDLE',
         os.path.join('ssl_certs', 'proxy_ca.crt'))
+    # Clear sessions to ensure that the certificate we just specified is used.
+    # TODO: Confirm necessity of this session clearing and lay out mechanics.
+    tuf.download._sessions = {}
 
     logger.info('Trying HTTPS download via HTTPS proxy: ' + self.url_https)
     download.safe_download(self.url_https, self.target_data_length)
@@ -325,7 +334,7 @@ def restore_env_value(self, key):
     assert key in self.old_env_values, 'Test coding mistake: something is ' \
         'trying to restore environment variable ' + key + ', but that ' \
         'variable does not appear in the list of values to restore. ' \
-        'Please make sure to use _set_env_value().'
+        'Please make sure to use set_env_value().'
 
     if self.old_env_values[key] is None:
       # If it was not previously set, try to unset it.