tests: look for ensurepip before using venv Debian appears to cripple the venv module by default by removing the associated ensurepip functionality. (The module isn't present at all.) This caused test-install.t to fail when using the Debian python3 unless the python3-venv package was installed. This commit introduces a new hghave requirement for detecting ensurepip and makes the Python 3 install variant conditional on its presence. This should make test-install.t pass when using an incomplete Debian Python. Differential Revision: https://phab.mercurial-scm.org/D7228

--- a/tests/hghave.py	Thu Oct 17 16:46:13 2019 -0400
+++ b/tests/hghave.py	Mon Nov 04 23:42:18 2019 -0800
@@ -829,6 +829,17 @@
     return os.path.exists('/dev/full')
 
 
+@check("ensurepip", "ensurepip module")
+def has_ensurepip():
+    try:
+        import ensurepip
+
+        ensurepip.bootstrap
+        return True
+    except ImportError:
+        return False
+
+
 @check("virtualenv", "Python virtualenv support")
 def has_virtualenv():
     try: