From 47e95486f05d8ec51831069ed24ed8694d964ee7 Mon Sep 17 00:00:00 2001
From: Joey Hain <jmhain@protonmail.com>
Date: Sat, 16 Feb 2019 08:50:45 -0800
Subject: [PATCH] Reuse and improve ergonomics of assert_raises utility

- Move assert_raises to testutils
- Add optional message argument, with reasonable default
- Reverse order of expr and exception type for readability
- Lambda argument no longer takes parameter
- Convert applicable snippets to use assert_raises
---
 tests/snippets/builtin_divmod.py       | 17 ++---
 tests/snippets/builtin_format.py       | 16 ++---
 tests/snippets/builtin_hex.py          |  9 +--
 tests/snippets/builtin_max.py          | 30 ++-------
 tests/snippets/builtin_min.py          | 31 ++-------
 tests/snippets/builtin_open.py         |  8 +--
 tests/snippets/builtin_ord.py          | 24 ++-----
 tests/snippets/builtin_range.py        | 31 ++-------
 tests/snippets/builtin_slice.py        |  8 +--
 tests/snippets/division_by_zero.py     | 62 +++---------------
 tests/snippets/division_of_big_ints.py | 16 ++---
 tests/snippets/floats.py               | 22 +------
 tests/snippets/func_defaults.py        | 90 ++++++++------------------
 tests/snippets/list.py                 | 30 ++-------
 tests/snippets/membership.py           | 16 ++---
 tests/snippets/printing.py             | 17 ++---
 tests/snippets/set.py                  | 17 ++---
 tests/snippets/stdlib_os.py            |  8 +--
 tests/snippets/test_bitwise.py         | 30 ++-------
 tests/snippets/testutils.py            | 20 ++++++
 20 files changed, 129 insertions(+), 373 deletions(-)
 create mode 100644 tests/snippets/testutils.py

diff --git a/tests/snippets/builtin_divmod.py b/tests/snippets/builtin_divmod.py
index 43b77a452..939e1d2d4 100644
--- a/tests/snippets/builtin_divmod.py
+++ b/tests/snippets/builtin_divmod.py
@@ -1,17 +1,8 @@
+from testutils import assert_raises
+
 assert divmod(11, 3) == (3, 2)
 assert divmod(8,11) == (0, 8)
 assert divmod(0.873, 0.252) == (3.0, 0.11699999999999999)
 
-try:
-    divmod(5, 0)
-except ZeroDivisionError:
-    pass
-else:
-    assert False, "Expected divmod by zero to throw ZeroDivisionError"
-
-try:
-    divmod(5.0, 0.0)
-except ZeroDivisionError:
-    pass
-else:
-    assert False, "Expected divmod by zero to throw ZeroDivisionError"
+assert_raises(ZeroDivisionError, lambda: divmod(5, 0), 'divmod by zero')
+assert_raises(ZeroDivisionError, lambda: divmod(5.0, 0.0), 'divmod by zero')
diff --git a/tests/snippets/builtin_format.py b/tests/snippets/builtin_format.py
index a811775e0..6c06cbd98 100644
--- a/tests/snippets/builtin_format.py
+++ b/tests/snippets/builtin_format.py
@@ -1,17 +1,9 @@
+from testutils import assert_raises
+
 assert format(5, "b") == "101"
 
-try:
-    format(2, 3)
-except TypeError:
-    pass
-else:
-    assert False, "TypeError not raised when format is called with a number"
+assert_raises(TypeError, lambda: format(2, 3), 'format called with number')
 
 assert format({}) == "{}"
 
-try:
-    format({}, 'b')
-except TypeError:
-    pass
-else:
-    assert False, "TypeError not raised when format_spec not empty for dict"
+assert_raises(TypeError, lambda: format({}, 'b'), 'format_spec not empty for dict')
diff --git a/tests/snippets/builtin_hex.py b/tests/snippets/builtin_hex.py
index b975e2186..f6f25ab58 100644
--- a/tests/snippets/builtin_hex.py
+++ b/tests/snippets/builtin_hex.py
@@ -1,9 +1,6 @@
+from testutils import assert_raises
+
 assert hex(16) == '0x10'
 assert hex(-16) == '-0x10'
 
-try:
-    hex({})
-except TypeError:
-    pass
-else:
-    assert False, "TypeError not raised when ord() is called with a dict"
+assert_raises(TypeError, lambda: hex({}), 'ord() called with dict')
diff --git a/tests/snippets/builtin_max.py b/tests/snippets/builtin_max.py
index 321aa6984..1494ecd80 100644
--- a/tests/snippets/builtin_max.py
+++ b/tests/snippets/builtin_max.py
@@ -1,3 +1,5 @@
+from testutils import assert_raises
+
 # simple values
 assert max(0, 0) == 0
 assert max(1, 0) == 1
@@ -14,32 +16,17 @@ assert max({
 }) == "b"
 assert max([1, 2], default=0) == 2
 assert max([], default=0) == 0
-try:
-    max([])
-except ValueError:
-    pass
-else:
-    assert False, "ValueError was not raised"
+assert_raises(ValueError, lambda: max([]))
 
 # key parameter
 assert max(1, 2, -3, key=abs) == -3
 assert max([1, 2, -3], key=abs) == -3
 
 # no argument
-try:
-    max()
-except TypeError:
-    pass
-else:
-    assert False, "TypeError was not raised"
+assert_raises(TypeError, lambda: max())
 
 # one non-iterable argument
-try:
-    max(1)
-except TypeError:
-    pass
-else:
-    assert False, "TypeError was not raised"
+assert_raises(TypeError, lambda: max(1))
 
 
 # custom class
@@ -64,9 +51,4 @@ class MyNotComparable():
     pass
 
 
-try:
-    max(MyNotComparable(), MyNotComparable())
-except TypeError:
-    pass
-else:
-    assert False, "TypeError was not raised"
+assert_raises(TypeError, lambda: max(MyNotComparable(), MyNotComparable()))
diff --git a/tests/snippets/builtin_min.py b/tests/snippets/builtin_min.py
index 77c9eaccf..ed45eff58 100644
--- a/tests/snippets/builtin_min.py
+++ b/tests/snippets/builtin_min.py
@@ -1,3 +1,5 @@
+from testutils import assert_raises
+
 # simple values
 assert min(0, 0) == 0
 assert min(1, 0) == 0
@@ -14,32 +16,18 @@ assert min({
 }) == "a"
 assert min([1, 2], default=0) == 1
 assert min([], default=0) == 0
-try:
-    min([])
-except ValueError:
-    pass
-else:
-    assert False, "ValueError was not raised"
+
+assert_raises(ValueError, lambda: min([]))
 
 # key parameter
 assert min(1, 2, -3, key=abs) == 1
 assert min([1, 2, -3], key=abs) == 1
 
 # no argument
-try:
-    min()
-except TypeError:
-    pass
-else:
-    assert False, "TypeError was not raised"
+assert_raises(TypeError, lambda: min())
 
 # one non-iterable argument
-try:
-    min(1)
-except TypeError:
-    pass
-else:
-    assert False, "TypeError was not raised"
+assert_raises(TypeError, lambda: min(1))
 
 
 # custom class
@@ -64,9 +52,4 @@ class MyNotComparable():
     pass
 
 
-try:
-    min(MyNotComparable(), MyNotComparable())
-except TypeError:
-    pass
-else:
-    assert False, "TypeError was not raised"
+assert_raises(TypeError, lambda: min(MyNotComparable(), MyNotComparable()))
diff --git a/tests/snippets/builtin_open.py b/tests/snippets/builtin_open.py
index 805c975c8..55eafcd6c 100644
--- a/tests/snippets/builtin_open.py
+++ b/tests/snippets/builtin_open.py
@@ -1,8 +1,6 @@
+from testutils import assert_raises
+
 fd = open('README.md')
 assert 'RustPython' in fd.read()
 
-try:
-    open('DoesNotExist')
-    assert False
-except FileNotFoundError:
-    pass
+assert_raises(FileNotFoundError, lambda: open('DoesNotExist'))
diff --git a/tests/snippets/builtin_ord.py b/tests/snippets/builtin_ord.py
index 2dd03f91a..2549f28e7 100644
--- a/tests/snippets/builtin_ord.py
+++ b/tests/snippets/builtin_ord.py
@@ -1,23 +1,9 @@
+from testutils import assert_raises
+
 assert ord("a") == 97
 assert ord("é") == 233
 assert ord("🤡") == 129313
-try:
-    ord()
-except TypeError:
-    pass
-else:
-    assert False, "TypeError not raised when ord() is called with no argument"
 
-try:
-    ord("")
-except TypeError:
-    pass
-else:
-    assert False, "TypeError not raised when ord() is called with an empty string"
-
-try:
-    ord("ab")
-except TypeError:
-    pass
-else:
-    assert False, "TypeError not raised when ord() is called with more than one character"
+assert_raises(TypeError, lambda: ord(), "ord() is called with no argument")
+assert_raises(TypeError, lambda: ord(""), "ord() is called with an empty string")
+assert_raises(TypeError, lambda: ord("ab"), "ord() is called with more than one character")
diff --git a/tests/snippets/builtin_range.py b/tests/snippets/builtin_range.py
index 6a20c6f1e..89014880c 100644
--- a/tests/snippets/builtin_range.py
+++ b/tests/snippets/builtin_range.py
@@ -1,20 +1,4 @@
-def assert_raises(expr, exc_type):
-    """
-    Helper function to assert `expr` raises an exception of type `exc_type`
-    Args:
-        expr: Callable
-        exec_type: Exception
-    Returns:
-        None
-    Raises:
-        Assertion error on failure
-    """
-    try:
-        expr(None)
-    except exc_type:
-        assert True
-    else:
-        assert False
+from testutils import assert_raises
 
 assert range(2**63+1)[2**63] == 9223372036854775808
 
@@ -29,15 +13,10 @@ assert range(4, 10).index(6) == 2
 assert range(4, 10, 2).index(6) == 1
 assert range(10, 4, -2).index(8) == 1
 
-# index raises value error on out of bounds
-assert_raises(lambda _: range(10).index(-1), ValueError)
-assert_raises(lambda _: range(10).index(10), ValueError)
-
-# index raises value error if out of step
-assert_raises(lambda _: range(4, 10, 2).index(5), ValueError)
-
-# index raises value error if needle is not an int
-assert_raises(lambda _: range(10).index('foo'), ValueError)
+assert_raises(ValueError, lambda: range(10).index(-1), 'out of bounds')
+assert_raises(ValueError, lambda: range(10).index(10), 'out of bounds')
+assert_raises(ValueError, lambda: range(4, 10, 2).index(5), 'out of step')
+assert_raises(ValueError, lambda: range(10).index('foo'), 'not an int')
 
 # count tests
 assert range(10).count(2) == 1
diff --git a/tests/snippets/builtin_slice.py b/tests/snippets/builtin_slice.py
index b7c3922c0..1d8a93b47 100644
--- a/tests/snippets/builtin_slice.py
+++ b/tests/snippets/builtin_slice.py
@@ -1,3 +1,4 @@
+from testutils import assert_raises
 
 a = []
 assert a[:] == []
@@ -18,12 +19,7 @@ assert b[-10:1] == [1]
 assert b[0:0] == []
 assert b[1:0] == []
 
-try:
-    _ = b[::0]
-except ValueError:
-    pass
-else:
-    assert False, "Zero step slice should raise ValueError"
+assert_raises(ValueError, lambda: b[::0], 'zero step slice')
 
 assert b[::-1] == [2, 1]
 assert b[1::-1] == [2, 1]
diff --git a/tests/snippets/division_by_zero.py b/tests/snippets/division_by_zero.py
index d92419d79..d8b900636 100644
--- a/tests/snippets/division_by_zero.py
+++ b/tests/snippets/division_by_zero.py
@@ -1,55 +1,11 @@
-try:
-    5 / 0
-except ZeroDivisionError:
-    pass
-else:
-    assert False, 'Expected ZeroDivisionError'
+from testutils import assert_raises
 
-try:
-    5 / -0.0
-except ZeroDivisionError:
-    pass
-else:
-    assert False, 'Expected ZeroDivisionError'
+assert_raises(ZeroDivisionError, lambda: 5 / 0)
+assert_raises(ZeroDivisionError, lambda: 5 / -0.0)
+assert_raises(ZeroDivisionError, lambda: 5 / (2-2))
+assert_raises(ZeroDivisionError, lambda: 5 % 0)
+assert_raises(ZeroDivisionError, lambda: 5 // 0)
+assert_raises(ZeroDivisionError, lambda: 5.3 // (-0.0))
+assert_raises(ZeroDivisionError, lambda: divmod(5, 0))
 
-try:
-    5 / (2-2)
-except ZeroDivisionError:
-    pass
-else:
-    assert False, 'Expected ZeroDivisionError'
-
-try:
-    5 % 0
-except ZeroDivisionError:
-    pass
-else:
-    assert False, 'Expected ZeroDivisionError'
-
-try:
-    5 // 0
-except ZeroDivisionError:
-    pass
-else:
-    assert False, 'Expected ZeroDivisionError'
-
-try:
-    5.3 // (-0.0)
-except ZeroDivisionError:
-    pass
-else:
-    assert False, 'Expected ZeroDivisionError'
-
-try:
-    divmod(5, 0)
-except ZeroDivisionError:
-    pass
-else:
-    assert False, 'Expected ZeroDivisionError'
-
-try:
-    raise ZeroDivisionError('Is an ArithmeticError subclass?')
-except ArithmeticError:
-    pass
-else:
-    assert False, 'Expected ZeroDivisionError'
+assert issubclass(ZeroDivisionError, ArithmeticError)
diff --git a/tests/snippets/division_of_big_ints.py b/tests/snippets/division_of_big_ints.py
index 466862219..9595ae603 100644
--- a/tests/snippets/division_of_big_ints.py
+++ b/tests/snippets/division_of_big_ints.py
@@ -1,3 +1,5 @@
+from testutils import assert_raises
+
 # 2.456984346552728
 res = 10**500 / (4 * 10**499 + 7 * 10**497 + 3 * 10**494)
 assert 2.456984 <= res <= 2.456985
@@ -8,20 +10,10 @@ assert 95.238095 <= res <= 95.238096
 
 assert 10**500 / (2*10**(500-308)) == 5e307
 assert 10**500 / (10**(500-308)) == 1e308
-try:
-    10**500 / (10**(500-309))
-except OverflowError:
-    pass
-else:
-    assert False, 'Expected overflow on too big result'
+assert_raises(OverflowError, lambda: 10**500 / (10**(500-309)), 'too big result')
 
 # a bit more than f64::MAX = 1.7976931348623157e+308_f64
 assert (2 * 10**308) / 2 == 1e308
 
 # when dividing too big int by a float, the operation should fail
-try:
-    (2 * 10**308) / 2.0
-except OverflowError:
-    pass
-else:
-    assert False, 'Expected overflow on division of a big int by a float'
+assert_raises(OverflowError, lambda: (2 * 10**308) / 2.0, 'division of big int by float')
diff --git a/tests/snippets/floats.py b/tests/snippets/floats.py
index 8f17c4bd5..003cf1ff0 100644
--- a/tests/snippets/floats.py
+++ b/tests/snippets/floats.py
@@ -1,22 +1,6 @@
 import math
 
-def assert_raises(expr, exc_type):
-    """
-    Helper function to assert `expr` raises an exception of type `exc_type`
-    Args:
-        expr: Callable
-        exec_type: Exception
-    Returns:
-        None
-    Raises:
-        Assertion error on failure
-    """
-    try:
-        expr(None)
-    except exc_type:
-        assert True
-    else:
-        assert False
+from testutils import assert_raises
 
 1 + 1.1
 
@@ -79,8 +63,8 @@ assert float('2.99e-23') == 2.99e-23
 assert float(b'3.14') == 3.14
 assert float(b'2.99e-23') == 2.99e-23
 
-assert_raises(lambda _: float('foo'), ValueError)
-assert_raises(lambda _: float(2**10000), OverflowError)
+assert_raises(ValueError, lambda: float('foo'))
+assert_raises(OverflowError, lambda: float(2**10000))
 
 # check that magic methods are implemented for ints and floats
 
diff --git a/tests/snippets/func_defaults.py b/tests/snippets/func_defaults.py
index a7d08c136..5fcf93047 100644
--- a/tests/snippets/func_defaults.py
+++ b/tests/snippets/func_defaults.py
@@ -1,21 +1,12 @@
+from testutils import assert_raises
+
 def no_args():
     pass
 
 no_args()
 
-try:
-    no_args('one_arg')
-except TypeError:
-    pass
-else:
-    assert False, 'no TypeError raised: 1 arg to no_args'
-
-try:
-    no_args(kw='should fail')
-except TypeError:
-    pass
-else:
-    assert False, 'no TypeError raised: kwarg to no_args'
+assert_raises(TypeError, lambda: no_args('one_arg'), '1 arg to no_args')
+assert_raises(TypeError, lambda: no_args(kw='should fail'), 'kwarg to no_args')
 
 
 def one_arg(arg):
@@ -24,40 +15,20 @@ def one_arg(arg):
 one_arg('one_arg')
 assert "arg" == one_arg(arg="arg")
 
-try:
-    one_arg()
-except TypeError:
-    pass
-else:
-    assert False, 'no TypeError raised: no args to one_arg'
+assert_raises(TypeError, lambda: one_arg(), 'no args to one_arg')
+assert_raises(TypeError,
+              lambda: one_arg(wrong_arg='wont work'),
+              'incorrect kwarg to one_arg')
+assert_raises(TypeError,
+              lambda: one_arg('one_arg', 'two_arg'),
+              'two args to one_arg')
+assert_raises(TypeError,
+              lambda: one_arg('one_arg', extra_arg='wont work'),
+              'no TypeError raised: extra kwarg to one_arg')
 
-try:
-    one_arg(wrong_arg='wont work')
-except TypeError:
-    pass
-else:
-    assert False, 'no TypeError raised: incorrect kwarg to one_arg'
-
-try:
-    one_arg('one_arg', 'two_arg')
-except TypeError:
-    pass
-else:
-    assert False, 'no TypeError raised: two args to one_arg'
-
-try:
-    one_arg('one_arg', extra_arg='wont work')
-except TypeError:
-    pass
-else:
-    assert False, 'no TypeError raised: extra kwarg to one_arg'
-
-try:
-    one_arg('one_arg', arg='duplicate')
-except TypeError:
-    pass
-else:
-    assert False, 'no TypeError raised: same pos and kwarg to one_arg'
+assert_raises(TypeError,
+              lambda: one_arg('one_arg', arg='duplicate'),
+              'same pos and kwarg to one_arg')
 
 
 def one_default_arg(arg="default"):
@@ -67,12 +38,9 @@ assert 'default' == one_default_arg()
 assert 'arg' == one_default_arg('arg')
 assert 'kwarg' == one_default_arg(arg='kwarg')
 
-try:
-    one_default_arg('one_arg', 'two_arg')
-except TypeError:
-    pass
-else:
-    assert False, 'no TypeError raised: two args to one_default_arg'
+assert_raises(TypeError,
+              lambda: one_default_arg('one_arg', 'two_arg'),
+              'two args to one_default_arg')
 
 
 def one_normal_one_default_arg(pos, arg="default"):
@@ -81,19 +49,13 @@ def one_normal_one_default_arg(pos, arg="default"):
 assert ('arg', 'default') == one_normal_one_default_arg('arg')
 assert ('arg', 'arg2') == one_normal_one_default_arg('arg', 'arg2')
 
-try:
-    one_normal_one_default_arg()
-except TypeError:
-    pass
-else:
-    assert False, 'no TypeError raised: no args to one_normal_one_default_arg'
+assert_raises(TypeError,
+              lambda: one_normal_one_default_arg(),
+              'no args to one_normal_one_default_arg')
 
-try:
-    one_normal_one_default_arg('one', 'two', 'three')
-except TypeError:
-    pass
-else:
-    assert False, 'no TypeError raised: three args to one_normal_one_default_arg'
+assert_raises(TypeError,
+              lambda: one_normal_one_default_arg('one', 'two', 'three'),
+              'three args to one_normal_one_default_arg')
 
 
 def two_pos(a, b):
diff --git a/tests/snippets/list.py b/tests/snippets/list.py
index 749d6c2bc..4bf6dd049 100644
--- a/tests/snippets/list.py
+++ b/tests/snippets/list.py
@@ -1,3 +1,5 @@
+from testutils import assert_raises
+
 x = [1, 2, 3]
 assert x[0] == 1
 assert x[1] == 2
@@ -16,12 +18,7 @@ assert x * 2 == [1, 2, 3, 1, 2, 3], "list __mul__ by 2 failed"
 # index()
 assert ['a', 'b', 'c'].index('b') == 1
 assert [5, 6, 7].index(7) == 2
-try:
-    ['a', 'b', 'c'].index('z')
-except ValueError:
-    pass
-else:
-    assert False, "ValueError was not raised"
+assert_raises(ValueError, lambda: ['a', 'b', 'c'].index('z'))
 
 x = [[1,0,-3], 'a', 1]
 y = [[3,2,1], 'z', 2]
@@ -33,12 +30,7 @@ assert x > y, "list __gt__ failed"
 
 
 assert [1,2,'a'].pop() == 'a', "list pop failed"
-try:
-    [].pop()
-except IndexError:
-    pass
-else:
-    assert False, "IndexError was not raised"
+assert_raises(IndexError, lambda: [].pop())
 
 recursive = []
 recursive.append(recursive)
@@ -61,12 +53,7 @@ x = ['a', 'b', 'c']
 x.insert(-100, 'z')
 assert x == ['z', 'a', 'b', 'c']
 
-try:
-    x.insert(100000000000000000000, 'z')
-except OverflowError:
-    pass
-else:
-    assert False, "OverflowError was not raised"
+assert_raises(OverflowError, lambda: x.insert(100000000000000000000, 'z'))
 
 x = [[], 2, {}]
 y = x.copy()
@@ -82,9 +69,4 @@ a.remove(1)
 assert len(a) == 2
 assert not 1 in a
 
-try:
-    a.remove(10)
-except ValueError:
-    pass
-else:
-    assert False, "Remove not exist element should raise ValueError"
+assert_raises(ValueError, lambda: a.remove(10), 'Remove not exist element')
diff --git a/tests/snippets/membership.py b/tests/snippets/membership.py
index 4c6fb3cae..a944c4539 100644
--- a/tests/snippets/membership.py
+++ b/tests/snippets/membership.py
@@ -1,3 +1,5 @@
+from testutils import assert_raises
+
 # test lists
 assert 3 in [1, 2, 3]
 assert 3 not in [1, 2]
@@ -19,12 +21,7 @@ assert b"5" <= b"5"
 assert b"4" > b"2"
 assert not b"1" >= b"2"
 assert b"10" >= b"10"
-try:
-    bytes() > 2
-except TypeError:
-    pass
-else:
-    assert False, "TypeError not raised"
+assert_raises(TypeError, lambda: bytes() > 2)
 
 # test tuple
 assert 1 in (1, 2)
@@ -53,12 +50,7 @@ class MyNotContainingClass():
     pass
 
 
-try:
-    1 in MyNotContainingClass()
-except TypeError:
-    pass
-else:
-    assert False, "TypeError not raised"
+assert_raises(TypeError, lambda: 1 in MyNotContainingClass())
 
 
 class MyContainingClass():
diff --git a/tests/snippets/printing.py b/tests/snippets/printing.py
index 2611e1387..e420c6c7f 100644
--- a/tests/snippets/printing.py
+++ b/tests/snippets/printing.py
@@ -1,18 +1,9 @@
+from testutils import assert_raises
+
 print(2 + 3)
 
-try:
-    print('test', end=4)
-except TypeError:
-    pass
-else:
-    assert False, 'Expected TypeError on wrong type passed to end'
-
-try:
-    print('test', sep=['a'])
-except TypeError:
-    pass
-else:
-    assert False, 'Expected TypeError on wrong type passed to sep'
+assert_raises(TypeError, lambda: print('test', end=4), 'wrong type passed to end')
+assert_raises(TypeError, lambda: print('test', sep=['a']), 'wrong type passed to sep')
 
 try:
     print('test', end=None, sep=None, flush=None)
diff --git a/tests/snippets/set.py b/tests/snippets/set.py
index 7a377fce3..f20c278e2 100644
--- a/tests/snippets/set.py
+++ b/tests/snippets/set.py
@@ -1,3 +1,5 @@
+from testutils import assert_raises
+
 assert set([1,2]) == set([1,2])
 assert not set([1,2,3]) == set([1,2])
 
@@ -69,19 +71,8 @@ assert set([1,2,3]).symmetric_difference(set([5,6])) == set([1,2,3,5,6])
 assert set([1,2,3]) ^ set([4,5]) == set([1,2,3,4,5])
 assert set([1,2,3]) ^ set([1,2,3,4,5]) == set([4,5])
 
-try:
-	set([[]])
-except TypeError:
-	pass
-else:
-	assert False, "TypeError was not raised"
-
-try:
-	set().add([])
-except TypeError:
-	pass
-else:
-	assert False, "TypeError was not raised"
+assert_raises(TypeError, lambda: set([[]]))
+assert_raises(TypeError, lambda: set().add([]))
 
 a = set([1, 2, 3])
 assert a.discard(1) is None
diff --git a/tests/snippets/stdlib_os.py b/tests/snippets/stdlib_os.py
index d8f03053f..ed9e91c70 100644
--- a/tests/snippets/stdlib_os.py
+++ b/tests/snippets/stdlib_os.py
@@ -1,13 +1,11 @@
 import os 
 
+from testutils import assert_raises
+
 assert os.open('README.md', 0) > 0
 
 
-try:
-    os.open('DOES_NOT_EXIST', 0)
-    assert False
-except FileNotFoundError:
-    pass
+assert_raises(FileNotFoundError, lambda: os.open('DOES_NOT_EXIST', 0))
 
 
 assert os.O_RDONLY == 0
diff --git a/tests/snippets/test_bitwise.py b/tests/snippets/test_bitwise.py
index 18b90a197..32028c996 100644
--- a/tests/snippets/test_bitwise.py
+++ b/tests/snippets/test_bitwise.py
@@ -1,20 +1,4 @@
-def assert_raises(expr, exc_type):
-    """
-    Helper function to assert `expr` raises an exception of type `exc_type`
-    Args:
-        expr: Callable
-        exec_type: Exception
-    Returns:
-        None
-    Raises:
-        Assertion error on failure
-    """
-    try:
-        expr(None)
-    except exc_type:
-        assert True
-    else:
-        assert False
+from testutils import assert_raises
 
 #
 # Tests
@@ -23,15 +7,15 @@ assert 8 >> 3 == 1
 assert 8 << 3 == 64
 
 # Left shift raises type error
-assert_raises(lambda _: 1 << 0.1, TypeError)
-assert_raises(lambda _: 1 << "abc", TypeError)
+assert_raises(TypeError, lambda: 1 << 0.1)
+assert_raises(TypeError, lambda: 1 << "abc")
 
 # Right shift raises type error
-assert_raises(lambda _: 1 >> 0.1, TypeError)
-assert_raises(lambda _: 1 >> "abc", TypeError)
+assert_raises(TypeError, lambda: 1 >> 0.1)
+assert_raises(TypeError, lambda: 1 >> "abc")
 
 # Left shift raises value error on negative
-assert_raises(lambda _: 1 << -1, ValueError)
+assert_raises(ValueError, lambda: 1 << -1)
 
 # Right shift raises value error on negative
-assert_raises(lambda _: 1 >> -1, ValueError)
+assert_raises(ValueError, lambda: 1 >> -1)
diff --git a/tests/snippets/testutils.py b/tests/snippets/testutils.py
new file mode 100644
index 000000000..b5b69b867
--- /dev/null
+++ b/tests/snippets/testutils.py
@@ -0,0 +1,20 @@
+def assert_raises(exc_type, expr, msg=None):
+    """
+    Helper function to assert `expr` raises an exception of type `exc_type`.
+    Args:
+        expr: Callable
+        exec_type: Exception
+    Returns:
+        None
+    Raises:
+        Assertion error on failure
+    """
+    try:
+        expr()
+    except exc_type:
+        pass
+    else:
+        failmsg = f'{exc_type.__name__} was not raised'
+        if msg is not None:
+            failmsg += f': {msg}'
+        assert False, failmsg