Fix crash on creation a regression test interactively

* Also create `is_interactive` function in `os_ext` to check whether
  the session is interactive.

* Add unittest for the above function.

Author: Theofilos Manitaras

reframe/core/pipeline.py

@@ -670,7 +670,10 @@ def __new__(cls, *args, **kwargs):
         try:
             prefix = cls._rfm_custom_prefix
         except AttributeError:
-            prefix = os.path.abspath(os.path.dirname(inspect.getfile(cls)))
+            if os_ext.is_interactive():
+                prefix = os.getcwd()
+            else:
+                prefix = os.path.abspath(os.path.dirname(inspect.getfile(cls)))
 
         obj._rfm_init(name, prefix)
         return obj

reframe/utility/os_ext.py

@@ -227,6 +227,11 @@ def inpath(entry, pathvar):
     return entry in set(pathvar.split(':'))
 
 
+def is_interactive():
+    '''Returns whether the given Python session is interactive'''
+    return bool(getattr(sys, 'ps1', sys.flags.interactive))
+
+
 def subdirs(dirname, recurse=False):
     '''Returns a list of dirname + its subdirectories. If recurse is True,
     recursion is performed in pre-order.'''

unittests/test_utility.py

@@ -173,6 +173,11 @@ def test_samefile(self):
                                os.path.join(prefix, 'broken1'))
         shutil.rmtree(prefix)
 
+    def test_is_interactive(self):
+        # Set `sys.ps1` to immitate an interactive session
+        sys.ps1 = 'rfm>>> '
+        assert os_ext.is_interactive()
+
     def test_is_url(self):
         repo_https = 'https://github.com/eth-cscs/reframe.git'
         repo_ssh = '[email protected]:eth-cscs/reframe.git'