[feat] Add a print() sanity function

reframe/utility/sanity.py

@@ -62,6 +62,7 @@
 import glob as pyglob
 import itertools
 import re
+import sys
 
 import reframe.utility as util
 from reframe.core.deferrable import deferrable, _DeferredExpression
@@ -182,6 +183,36 @@ def min(*args):
     return builtins.min(*args)
 
 
+@deferrable
+def print(*objects, sep=' ', end='\n', file=None, flush=False):
+    '''Replacement for the built-in :func:`print() <python:print>` function.
+
+    The only difference is that this function returns the ``objects``, so that
+    you can use it transparently inside a complex sanity expression. For
+    example, you could write the following to print the matches returned from
+    the :func:`extractall()` function:
+
+    .. code:: python
+
+        self.sanity_patterns = sn.assert_eq(
+            sn.count(sn.print(sn.extract_all(...))), 10
+        )
+
+    If ``file`` is None, :func:`print` will print its arguments to the
+    standard output. Unlike the builtin :func:`print() <python:print>`
+    function, we don't bind the ``file`` argument to :attr:`sys.stdout` by
+    default. This would capture :attr:`sys.stdout` at the time this function
+    is defined and would prevent it from seeing changes to :attr:`sys.stdout`,
+    such as redirects, in the future.
+    '''
+
+    if file is None:
+        file = sys.stdout
+
+    builtins.print(*objects, sep=sep, end=end, file=file, flush=flush)
+    return objects
+
+
 @deferrable
 def reversed(seq):
     '''Replacement for the built-in

unittests/test_sanity_functions.py

@@ -1,8 +1,13 @@
+import contextlib
+import io
 import itertools
 import os
+import sys
 import unittest
+
 from tempfile import NamedTemporaryFile
 
+
 import reframe.utility.sanity as sn
 from reframe.core.exceptions import SanityError
 from unittests.fixtures import TEST_RESOURCES_CHECKS
@@ -124,6 +129,42 @@ def test_min(self):
         l.append(0)
         self.assertEqual(0, sn.min(dl))
 
+    def test_print_stdout(self):
+        stdout = io.StringIO()
+        with contextlib.redirect_stdout(stdout):
+            x, y = sn.evaluate(sn.print(1, sn.defer(2)))
+
+        assert stdout.getvalue() == '1 2\n'
+        assert x == 1
+        assert y == 2
+
+    def test_print_stderr(self):
+        stderr = io.StringIO()
+        with contextlib.redirect_stderr(stderr):
+            x, y = sn.evaluate(sn.print(1, sn.defer(2), file=sys.stderr))
+
+        assert stderr.getvalue() == '1 2\n'
+        assert x == 1
+        assert y == 2
+
+    def test_print_separator(self):
+        stdout = io.StringIO()
+        with contextlib.redirect_stdout(stdout):
+            x, y = sn.evaluate(sn.print(1, sn.defer(2), sep='|'))
+
+        assert stdout.getvalue() == '1|2\n'
+        assert x == 1
+        assert y == 2
+
+    def test_print_end(self):
+        stdout = io.StringIO()
+        with contextlib.redirect_stdout(stdout):
+            x, y = sn.evaluate(sn.print(1, sn.defer(2), end=''))
+
+        assert stdout.getvalue() == '1 2'
+        assert x == 1
+        assert y == 2
+
     def test_reversed(self):
         l = [1, 2, 3]
         dr = sn.reversed(l)