tests: actually check that HGDEMANDIMPORT=disable disables demandimport

tests: actually check that HGDEMANDIMPORT=disable disables demandimport

At the point in the test where we were checking that the 'node' got
eagerly loaded, it had already been loaded (via the pvec module), so
our check wasn't doing anything (i.e. the test would pass even if you
removed the line that set HGDEMANDIMPORT=disable). Let's move this
test earlier so it tests what it was meant to test.

Differential Revision: https://phab.mercurial-scm.org/D2286

--- a/tests/test-demandimport.py	Thu Jan 04 16:29:07 2018 -0800
+++ b/tests/test-demandimport.py	Fri Feb 16 11:30:18 2018 -0800
@@ -31,6 +31,16 @@
     l = rsub("'<[a-z]*>'", "'<whatever>'", l)
     return l
 
+demandimport.disable()
+os.environ['HGDEMANDIMPORT'] = 'disable'
+# this enable call should not actually enable demandimport!
+demandimport.enable()
+from mercurial import node
+print("node =", f(node))
+# now enable it for real
+del os.environ['HGDEMANDIMPORT']
+demandimport.enable()
+
 import os
 
 print("os =", f(os))
@@ -97,10 +107,3 @@
 print("__import__('contextlib', ..., ['unknownattr']) =", f(contextlibimp))
 print("hasattr(contextlibimp, 'unknownattr') =",
       util.safehasattr(contextlibimp, 'unknownattr'))
-
-demandimport.disable()
-os.environ['HGDEMANDIMPORT'] = 'disable'
-# this enable call should not actually enable demandimport!
-demandimport.enable()
-from mercurial import node
-print("node =", f(node))

--- a/tests/test-demandimport.py.out	Thu Jan 04 16:29:07 2018 -0800
+++ b/tests/test-demandimport.py.out	Fri Feb 16 11:30:18 2018 -0800
@@ -1,3 +1,4 @@
+node = <module 'mercurial.node' from '?'>
 os = <unloaded module 'os'>
 os.system = <built-in function system>
 os = <module 'os' from '?'>
@@ -27,4 +28,3 @@
 contextlib.unknownattr = ImportError: cannot import name unknownattr
 __import__('contextlib', ..., ['unknownattr']) = <module 'contextlib' from '?'>
 hasattr(contextlibimp, 'unknownattr') = False
-node = <module 'mercurial.node' from '?'>