1Test::Fatal(3) User Contributed Perl Documentation Test::Fatal(3)
2
6 Test::Fatal - incredibly simple helpers for testing code with
7 exceptions
8
10 version 0.016
11
13 use Test::More;
14 use Test::Fatal;
15 use System::Under::Test qw(might_die);
17 is(
19 exception { might_die; },
20 undef,
21 "the code lived",
22 );
23 like(
25 exception { might_die; },
26 qr/turns out it died/,
27 "the code died as expected",
28 );
29 isa_ok(
31 exception { might_die; },
32 'Exception::Whatever',
33 'the thrown exception',
34 );
35
37 Test::Fatal is an alternative to the popular Test::Exception. It does
38 much less, but should allow greater flexibility in testing exception-
39 throwing code with about the same amount of typing.
40 It exports one routine by default: "exception".
42 Achtung! "exception" intentionally does not manipulate the call stack.
44 User-written test functions that use "exception" must be careful to
45 avoid false positives if exceptions use stack traces that show
46 arguments. For a more magical approach involving globally overriding
47 "caller", see Test::Exception.
48
50 exception
51 my $exception = exception { ... };
52 "exception" takes a bare block of code and returns the exception thrown
54 by that block. If no exception was thrown, it returns undef.
55 Achtung! If the block results in a false exception, such as 0 or the
57 empty string, Test::Fatal itself will die. Since either of these cases
58 indicates a serious problem with the system under testing, this
59 behavior is considered a feature. If you must test for these
60 conditions, you should use Try::Tiny's try/catch mechanism. (Try::Tiny
61 is the underlying exception handling system of Test::Fatal.)
62 Note that there is no TAP assert being performed. In other words, no
64 "ok" or "not ok" line is emitted. It's up to you to use the rest of
65 "exception" in an existing test like "ok", "isa_ok", "is", et cetera.
66 Or you may wish to use the "dies_ok" and "lives_ok" wrappers, which do
67 provide TAP output.
68 "exception" does not alter the stack presented to the called block,
70 meaning that if the exception returned has a stack trace, it will
71 include some frames between the code calling "exception" and the thing
72 throwing the exception. This is considered a feature because it avoids
73 the occasionally twitchy "Sub::Uplevel" mechanism.
74 Achtung! This is not a great idea:
76 sub exception_like(&$;$) {
78 my ($code, $pattern, $name) = @_;
79 like( &exception($code), $pattern, $name );
80 }
81 exception_like(sub { }, qr/foo/, 'foo appears in the exception');
83 If the code in the "..." is going to throw a stack trace with the
85 arguments to each subroutine in its call stack (for example via
86 "Carp::confess", the test name, "foo appears in the exception" will
87 itself be matched by the regex. Instead, write this:
88 like( exception { ... }, qr/foo/, 'foo appears in the exception' );
90 If you really want a test function that passes the test name, wrap the
92 arguments in an array reference to hide the literal text from a stack
93 trace:
94 sub exception_like(&$) {
96 my ($code, $args) = @_;
97 my ($pattern, $name) = @$args;
98 like( &exception($code), $pattern, $name );
99 }
100 exception_like(sub { }, [ qr/foo/, 'foo appears in the exception' ] );
102 To aid in avoiding the problem where the pattern is seen in the
104 exception because of the call stack, $Carp::MAxArgNums is locally set
105 to -1 when the code block is called. If you really don't want that,
106 set it back to whatever value you like at the beginning of the code
107 block. Obviously, this solution doens't affect all possible ways that
108 args of subroutines in the call stack might taint the test. The
109 intention here is to prevent some false passes from people who didn't
110 read the documentation. Your punishment for reading it is that you
111 must consider whether to do anything about this.
112 Achtung: One final bad idea:
114 isnt( exception { ... }, undef, "my code died!");
116 It's true that this tests that your code died, but you should really
118 test that it died for the right reason. For example, if you make an
119 unrelated mistake in the block, like using the wrong dereference, your
120 test will pass even though the code to be tested isn't really run at
121 all. If you're expecting an inspectable exception with an identifier
122 or class, test that. If you're expecting a string exception, consider
123 using "like".
124 success
126 try {
127 should_live;
128 } catch {
129 fail("boo, we died");
130 } success {
131 pass("hooray, we lived");
132 };
133 "success", exported only by request, is a Try::Tiny helper with
135 semantics identical to "finally", but the body of the block will only
136 be run if the "try" block ran without error.
137 Although almost any needed exception tests can be performed with
139 "exception", success blocks may sometimes help organize complex
140 testing.
141 dies_ok
143 lives_ok
144 Exported only by request, these two functions run a given block of
145 code, and provide TAP output indicating if it did, or did not throw an
146 exception. These provide an easy upgrade path for replacing existing
147 unit tests based on "Test::Exception".
148 RJBS does not suggest using this except as a convenience while porting
150 tests to use Test::Fatal's "exception" routine.
151 use Test::More tests => 2;
153 use Test::Fatal qw(dies_ok lives_ok);
154 dies_ok { die "I failed" } 'code that fails';
156 lives_ok { return "I'm still alive" } 'code that does not fail';
158
160 Ricardo Signes <rjbs@cpan.org>
161
163 • David Golden <dagolden@cpan.org>
164 • Graham Knop <haarg@haarg.org>
166 • Jesse Luehrs <doy@tozt.net>
168 • Joel Bernstein <joel@fysh.org>
170 • Karen Etheridge <ether@cpan.org>
172
174 This software is copyright (c) 2010 by Ricardo Signes.
175 This is free software; you can redistribute it and/or modify it under
177 the same terms as the Perl 5 programming language system itself.
178perl v5.36.0 2022-07-22 Test::Fatal(3)