Disable Mercurial Tests on Travis

tests/lib/__init__.py

@@ -789,6 +789,13 @@ def need_bzr(fn):
 
 
 def need_mercurial(fn):
+    # Remove once things get fixed properly.
+    if os.environ.get("TRAVIS") == "true":
+        return pytest.mark.skip(reason=(
+            "Travis CI's mercurial is outdated: "
+            "https://github.com/pypa/pip/issues/6057"
+        ))
+
     return pytest.mark.mercurial(need_executable(
         'Mercurial', ('hg', 'version')
     )(fn))

tox.ini

@@ -10,7 +10,8 @@ envlist =
 pip = python {toxinidir}/tools/tox_pip.py
 
 [testenv]
-passenv = CI GIT_SSL_CAINFO
+# NOTE: remove TRAVIS once #6057 is fixed.
+passenv = CI TRAVIS GIT_SSL_CAINFO
 setenv =
     # This is required in order to get UTF-8 output inside of the subprocesses
     # that our tests use.