tests/extmod/urandom: Add urandom tests for error cases.

tests/extmod/urandom_basic.py

@@ -17,3 +17,9 @@ random.seed(1)
 r = random.getrandbits(16)
 random.seed(1)
 print(random.getrandbits(16) == r)
+
+# check that it throws an error for zero bits
+try:
+    random.getrandbits(0)
+except ValueError:
+    print('ValueError')

tests/extmod/urandom_extra.py

@@ -16,6 +16,31 @@ for i in range(50):
     assert 2 <= random.randrange(2, 6) < 6
     assert -2 <= random.randrange(-2, 2) < 2
     assert random.randrange(1, 9, 2) in (1, 3, 5, 7)
+    assert random.randrange(2, 1, -1) in (1, 2)
+
+# empty range
+try:
+    random.randrange(0)
+except ValueError:
+    print('ValueError')
+
+# empty range
+try:
+    random.randrange(2, 1)
+except ValueError:
+    print('ValueError')
+
+# zero step
+try:
+    random.randrange(2, 1, 0)
+except ValueError:
+    print('ValueError')
+
+# empty range
+try:
+    random.randrange(2, 1, 1)
+except ValueError:
+    print('ValueError')
 
 print('randint')
 for i in range(50):
@@ -23,11 +48,23 @@ for i in range(50):
     assert 2 <= random.randint(2, 6) <= 6
     assert -2 <= random.randint(-2, 2) <= 2
 
+# empty range
+try:
+    random.randint(2, 1)
+except ValueError:
+    print('ValueError')
+
 print('choice')
 lst = [1, 2, 5, 6]
 for i in range(50):
     assert random.choice(lst) in lst
 
+# empty sequence
+try:
+    random.choice([])
+except IndexError:
+    print('IndexError')
+
 print('random')
 for i in range(50):
     assert 0 <= random.random() < 1