py3: replace print() with assert in test-demandimport.py

Behavior of demand imports behaves differently between Python 2 and 3.
.out files do not support conditional output the way that .t files do.
In order to make this test work on Python 3, we'll need to make the
test itself conditional.

The first step of this is to port the test to not use a .out file
to compare output.

Unfortunately, we can't easily use the unittest framework for
defining this test because putting import statements in functions
changes the behavior of the demand importer (at least on Python 2).
So, we effectively replace a bunch of print() with assert statements.

This makes the test a bit annoying to debug, as the test will
stop at first assertion failure. But we don't exactly have
a good alternative.

Differential Revision: https://phab.mercurial-scm.org/D5795

tests/test-demandimport.py

@@ -12,6 +12,10 b" if subprocess.call(['python', '%s/hghave"
                     'demandimport']):
     sys.exit(80)
 
+# We rely on assert, which gets optimized out.
+if sys.flags.optimize:
+    sys.exit(80)
+
 if os.name != 'nt':
     try:
         import distutils.msvc9compiler
@@ -36,69 +40,80 b" os.environ['HGDEMANDIMPORT'] = 'disable'"
 # this enable call should not actually enable demandimport!
 demandimport.enable()
 from mercurial import node
-print("node =", f(node))
+
+# We use assert instead of a unittest test case because having imports inside
+# functions changes behavior of the demand importer.
+assert f(node) == "<module 'mercurial.node' from '?'>", f(node)
+
 # now enable it for real
 del os.environ['HGDEMANDIMPORT']
 demandimport.enable()
 
 # Test access to special attributes through demandmod proxy
 from mercurial import error as errorproxy
-print("errorproxy =", f(errorproxy))
-print("errorproxy.__doc__ = %r"
-      % (' '.join(errorproxy.__doc__.split()[:3]) + ' ...'))
-print("errorproxy.__name__ = %r" % errorproxy.__name__)
+assert f(errorproxy) == "<unloaded module 'error'>", f(errorproxy)
+doc = ' '.join(errorproxy.__doc__.split()[:3])
+assert doc == 'Mercurial exceptions. This', doc
+assert errorproxy.__name__ == 'mercurial.error', errorproxy.__name__
+
 # __name__ must be accessible via __dict__ so the relative imports can be
 # resolved
-print("errorproxy.__dict__['__name__'] = %r" % errorproxy.__dict__['__name__'])
-print("errorproxy =", f(errorproxy))
+name = errorproxy.__dict__['__name__']
+assert name == 'mercurial.error', name
+
+assert f(errorproxy) == "<proxied module 'error'>", f(errorproxy)
 
 import os
 
-print("os =", f(os))
-print("os.system =", f(os.system))
-print("os =", f(os))
+assert f(os) == "<unloaded module 'os'>", f(os)
+assert f(os.system) == '<built-in function system>', f(os.system)
+assert f(os) == "<module 'os' from '?'>", f(os)
 
 from mercurial.utils import procutil
 
-print("procutil =", f(procutil))
-print("procutil.system =", f(procutil.system))
-print("procutil =", f(procutil))
-print("procutil.system =", f(procutil.system))
+assert f(procutil) == "<unloaded module 'procutil'>", f(procutil)
+assert f(procutil.system) == '<function system at 0x?>', f(procutil.system)
+assert f(procutil) == "<module 'mercurial.utils.procutil' from '?'>", f(
+    procutil
+)
+assert f(procutil.system) == '<function system at 0x?>', f(procutil.system)
 
 from mercurial import hgweb
-print("hgweb =", f(hgweb))
-print("hgweb_mod =", f(hgweb.hgweb_mod))
-print("hgweb =", f(hgweb))
+assert f(hgweb) == "<unloaded module 'hgweb'>", f(hgweb)
+assert f(hgweb.hgweb_mod) == "<unloaded module 'hgweb_mod'>", f(hgweb.hgweb_mod)
+assert f(hgweb) == "<module 'mercurial.hgweb' from '?'>", f(hgweb)
 
 import re as fred
-print("fred =", f(fred))
+assert f(fred) == "<unloaded module 're'>", f(fred)
 
 import re as remod
-print("remod =", f(remod))
+assert f(remod) == "<unloaded module 're'>", f(remod)
 
 import sys as re
-print("re =", f(re))
+assert f(re) == "<unloaded module 'sys'>", f(re)
 
-print("fred =", f(fred))
-print("fred.sub =", f(fred.sub))
-print("fred =", f(fred))
+assert f(fred) == "<unloaded module 're'>", f(fred)
+assert f(fred.sub) == '<function sub at 0x?>', f(fred.sub)
+assert f(fred) == "<proxied module 're'>", f(fred)
 
 remod.escape  # use remod
-print("remod =", f(remod))
+assert f(remod) == "<module 're' from '?'>", f(remod)
 
-print("re =", f(re))
-print("re.stderr =", f(re.stderr))
-print("re =", f(re))
+assert f(re) == "<unloaded module 'sys'>", f(re)
+assert f(re.stderr) == "<open file '<whatever>', mode 'w' at 0x?>", f(re.stderr)
+assert f(re) == "<proxied module 'sys'>", f(re)
 
 import contextlib
-print("contextlib =", f(contextlib))
+assert f(contextlib) == "<unloaded module 'contextlib'>", f(contextlib)
 try:
     from contextlib import unknownattr
-    print('no demandmod should be created for attribute of non-package '
-          'module:\ncontextlib.unknownattr =', f(unknownattr))
+
+    assert False, (
+        'no demandmod should be created for attribute of non-package '
+        'module:\ncontextlib.unknownattr = %s' % f(unknownattr)
+    )
 except ImportError as inst:
-    print('contextlib.unknownattr = ImportError: %s'
-          % rsub(r"'", '', str(inst)))
+    assert rsub(r"'", '', str(inst)) == 'cannot import name unknownattr'
 
 from mercurial import util
 
@@ -106,6 +121,5 b' from mercurial import util'
 # ImportError even if fromlist has an unknown item
 # (see Python/import.c:import_module_level() and ensure_fromlist())
 contextlibimp = __import__('contextlib', globals(), locals(), ['unknownattr'])
-print("__import__('contextlib', ..., ['unknownattr']) =", f(contextlibimp))
-print("hasattr(contextlibimp, 'unknownattr') =",
-      util.safehasattr(contextlibimp, 'unknownattr'))
+assert f(contextlibimp) == "<module 'contextlib' from '?'>", f(contextlibimp)
+assert not util.safehasattr(contextlibimp, 'unknownattr')