tests/extmod: Move split-on-empty-match tests to a separate test file.

And provide an expected-output file because these tests have a different
behaviour under CPython.

tests/extmod/ure_split.py

@@ -19,16 +19,6 @@ r = re.compile(" +")
 s = r.split("a b    c   foobar", 2)
 print(s)
 
-r = re.compile(" *")
-s = r.split("a b    c   foobar")
-# TODO - no idea how this is supposed to work, per docs, empty match == stop
-# splitting, so CPython code apparently does some dirty magic.
-#print(s)
-
-r = re.compile("x*")
-s = r.split("foo")
-print(s)
-
 r = re.compile("[a-f]+")
 s = r.split("0a3b9")
 print(s)

tests/extmod/ure_split_empty.py

@@ -0,0 +1,19 @@
+# test splitting with pattern matches that can be empty
+#
+# CPython 3.5 issues a FutureWarning for these tests because their
+# behaviour will change in a future version.  MicroPython just stops
+# splitting as soon as an empty match is found.
+
+import ure as re
+
+r = re.compile(" *")
+s = r.split("a b    c   foobar")
+print(s)
+
+r = re.compile("x*")
+s = r.split("foo")
+print(s)
+
+r = re.compile("x*")
+s = r.split("axbc")
+print(s)

tests/extmod/ure_split_empty.py.exp

@@ -0,0 +1,3 @@
+['a b    c   foobar']
+['foo']
+['axbc']