src/sage/env.py: Fix up doctest on starting sage without SAGE_* variables

Author: Matthias Koeppe

src/sage/env.py

@@ -5,14 +5,15 @@
 
 - \R. Andrew Ohana (2012): Initial version.
 
-Verify that Sage can be started without any ``SAGE_`` environment
-variables::
+Verify that importing ``sage.all`` works in Sage's Python without any ``SAGE_``
+environment variables, and has the same ``SAGE_ROOT`` and ``SAGE_LOCAL``::
 
     sage: env = {k:v for (k,v) in os.environ.items() if not k.startswith("SAGE_")}
-    sage: import subprocess
-    sage: cmd = "from sage.all import SAGE_ROOT; print(SAGE_ROOT)"
-    sage: res = subprocess.call([sys.executable, "-c", cmd], env=env)  # long time
-    None
+    sage: from subprocess import check_output
+    sage: cmd = "from sage.all import SAGE_ROOT, SAGE_LOCAL; print((SAGE_ROOT, SAGE_LOCAL))"
+    sage: out = check_output([sys.executable, "-c", cmd], env=env).decode().strip()   # long time
+    sage: out == repr((SAGE_ROOT, SAGE_LOCAL))                                        # long time
+    True
 """
 
 # ****************************************************************************