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Test::MockObject(3) |
User Contributed Perl Documentation |
Test::MockObject(3) |
Test::MockObject - Perl extension for emulating troublesome interfaces
use Test::MockObject;
my $mock = Test::MockObject->new();
$mock->set_true( 'somemethod' );
ok( $mock->somemethod() );
$mock->set_true( 'veritas')
->set_false( 'ficta' )
->set_series( 'amicae', 'Sunny', 'Kylie', 'Bella' );
It's a simple program that doesn't use any other modules, and those are easy to
test. More often, testing a program completely means faking up input to
another module, trying to coax the right output from something you're not
supposed to be testing anyway.
Testing is a lot easier when you can control the entire
environment. With Test::MockObject, you can get a lot closer.
Test::MockObject allows you to create objects that conform to
particular interfaces with very little code. You don't have to reimplement
the behavior, just the input and the output.
Before you go wild with your testing powers, consider three caveats:
- It is possible to write highly detailed unit tests that pass even when
your integration tests may fail. Testing the pieces individually does not
excuse you from testing the whole thing together.
- In cases where you only need to mock one or two pieces of an existing
module, consider Test::MockObject::Extends instead.
- If the code under testing produces strange errors about type checks, pass
the "-debug" flag when using
"Test::MockObject" or
"Test::MockObject::Extends". This will
load both UNIVERSAL::isa and UNIVERSAL::can to perform additional
debugging on the incorrect use of both methods from the UNIVERSAL package.
(This behavior used to be active by default, but that was, however
correct, probably a burden to onerous for the CPAN.)
The most important thing a Mock Object can do is to conform sufficiently to an
interface. For example, if you're testing something that relies on CGI.pm, you
may find it easier to create a mock object that returns controllable results
at given times than to fake query string input.
The Basics
- •
- "new"
Creates a new mock object. By default, this is a blessed hash.
Pass a reference to bless that reference.
my $mock_array = Test::MockObject->new( [] );
my $mock_scalar = Test::MockObject->new( \( my $scalar ) );
my $mock_code = Test::MockObject->new( sub {} );
my $mock_glob = Test::MockObject->new( \*GLOB );
Mocking
Your mock object is nearly useless if you don't tell it what it's
mocking. This is done by installing methods. You control the output of these
mocked methods. In addition, any mocked method is tracked. You can tell not
only what was called, but which arguments were passed. Please note that you
cannot track non-mocked method calls. They will still be allowed, though
Test::MockObject will carp() about them. This is considered a
feature, though it may be possible to disable this in the future.
As implied in the example above, it's possible to chain these
calls together. Thanks to a suggestion from the fabulous Piers Cawley (CPAN
RT #1249), this feature came about in version 0.09. Shorter testing code is
nice!
- "mock(name,
coderef [,
name2,
coderef2, ...])"
Adds one or more coderefs to the object. This allows code to
call the named methods on the object. For example, this code:
my $mock = Test::MockObject->new();
$mock->mock( 'fluorinate',
sub { 'impurifying precious bodily fluids' } );
print $mock->fluorinate;
will print a helpful warning message. Please note that methods
are only added to a single object at a time and not the class. (There is
no small similarity to the Self programming language or the
Class::Prototyped module.)
This method forms the basis for most of Test::MockObject's
testing goodness.
Please Note: this method used to be
"add()". Due to its ambiguity, it now
has a different spelling. For backwards compatibility purposes,
add() is available, though version 0.07 deprecated it. It goes to
some contortions to try to do what you mean, but I make few
guarantees.
- "fake_module(module
name), [ subname
=" coderef, ... ]
Note: See Test::MockModule for an alternate (and
better) approach.
Lies to Perl that it has already loaded a named module. This
is handy when providing a mockup of a real module if you'd like to
prevent the actual module from interfering with the nice fakery. If
you're mocking Regexp::English, say:
$mock->fake_module( 'Regexp::English' );
This is both a class and as an object method. Beware that this
must take place before the actual module has a chance to load. Either
wrap it in a BEGIN block before a use or require or place it before a
"use_ok()" or
"require_ok()" call.
You can optionally add functions to the mocked module by
passing them as name => coderef pairs to
"fake_module()". This is handy if you
want to test an "import()":
my $import;
$mock->fake_module(
'Regexp::English',
import => sub { $import = caller }
);
use_ok( 'Regexp::Esperanto' );
is( $import, 'Regexp::Esperanto',
'Regexp::Esperanto should use() Regexp::English' );
If you use "fake_module()"
to mock a module that already exists in memory -- one you've loaded
elsewhere perhaps, but do not pass any subroutines to mock, this method
will throw an exception. This is because if you call the constructor
later on, you probably won't get a mock object back and you'll be
confused.
- "fake_new(module
name)"
Note: see Test::MockObject::Extends for a better
alternative to this method.
Provides a fake constructor for the given module that returns
the invoking mock object. Used in conjunction with
"fake_module()", you can force the
tested unit to work with the mock object instead.
$mock->fake_module( 'CGI' );
$mock->fake_new( 'CGI' );
use_ok( 'Some::Module' );
my $s = Some::Module->new();
is( $s->{_cgi}, $mock,
'new() should create and store a new CGI object' );
- "set_always(name,
value)"
Adds a method of the specified name that always returns the
specified value.
- "set_true(name_1,
name_2, ...
name_n)"
Adds a method of the specified name that always returns a true
value. This can take a list of names.
- "set_false(name_1,
name_2, ...
name_n)"
Adds a method of the specified name that always returns a
false value. (Since it installs an empty subroutine, the value should be
false in both scalar and list contexts.) This can take a list of
names.
- "set_list(name, [
item1,
item2, ... ]"
Adds a method that always returns a given list of values. It
takes some care to provide a list and not an array, if that's important
to you.
- "set_series(name, [
item1,
item2, ... ]"
Adds a method that will return the next item in a series on
each call. This can help to test error handling, by forcing a failure on
the first method call and then subsequent successes. Note that the
series does not repeat; it will eventually run out.
- "set_bound(name,
reference)"
Adds a method bound to a variable. Pass in a reference to a
variable in your test. When you change the variable, the return value of
the new method will change as well. This is often handier than replacing
mock methods.
- "set_isa( name1,
name2, ...
namen )"
Adds an apparent parent to the module, so that calling
"isa()" on the mock will return true
appropriately. Sometimes you really need this.
- "remove(name)"
Removes a named method.
Checking Your Mocks
- "can( $method_name )"
Returns a subroutine reference if this particular mocked
object can handle the named method, false otherwise.
- "isa( $class_name )"
Returns true if the invocant object mocks a particular class.
You must have used "set_isa()"
first.
- "called(name)"
Checks to see if something has called a named method on the
object. This returns a boolean value. The current implementation does
not scale especially well, so use this sparingly if you need to search
through hundreds of calls.
- "clear()"
Clears the internal record of all method calls on the object.
It's handy to do this every now and then. Note that this does not affect
the mocked methods, only all of the methods called on the object to this
point.
It's handy to "clear()"
methods in between series of tests. That makes it much easier to call
"next_method()" without having to skip
over the calls from the last set of tests.
- "next_call([ position
])"
Returns the name and argument list of the next mocked method
called on an object, in list context. In scalar context, returns only
the method name. There are two important things to know about this
method. First, it starts at the beginning of the call list. If your code
runs like this:
$mock->set_true( 'foo' );
$mock->set_true( 'bar' );
$mock->set_true( 'baz' );
$mock->foo();
$mock->bar( 3, 4 );
$mock->foo( 1, 2 );
Then you might see output of:
my ($name, $args) = $mock->next_call();
print "$name (@$args)";
# prints 'foo'
$name = $mock->next_call();
print $name;
# prints 'bar'
($name, $args) = $mock->next_call();
print "$name (@$args)";
# prints 'foo 1 2'
If you provide an optional number as the position
argument, the method will skip that many calls, returning the data for
the last one skipped.
$mock->foo();
$mock->bar();
$mock->baz();
$name = $mock->next_call();
print $name;
# prints 'foo'
$name = $mock->next_call( 2 );
print $name
# prints 'baz'
When it reaches the end of the list, it returns undef. This is
probably the most convenient method in the whole module, but for the
sake of completeness and backwards compatibility (it takes me a while to
reach the truest state of laziness!), there are several other
methods.
- "call_pos(position)"
Returns the name of the method called on the object at a
specified position. This is handy if you need to test a certain order of
calls. For example:
Some::Function( $mock );
is( $mock->call_pos(1), 'setup',
'Function() should first call setup()' );
is( $mock->call_pos(-1), 'end',
'... and last call end()' );
Positions can be positive or negative. Please note that the
first position is, in fact, 1. (This may change in the future. I like
it, but am willing to reconsider.)
- "call_args(position)"
Returns a list of the arguments provided to the method called
at the appropriate position. Following the test above, one might
say:
is( ($mock->call_args(1))[0], $mock,
'... passing the object to setup()' );
is( scalar $mock->call_args(-1), 0,
'... and no args to end()' );
- "call_args_pos(call
position, argument
position)"
Returns the argument at the specified position for the method
call at the specified position. One might rewrite the first test of the
last example as:
is( $mock->call_args_pos(1, 1), $mock,
'... passing the object to setup()');
- "call_args_string(position,
[ separator ])"
Returns a stringified version of the arguments at the
specified position. If no separator is given, they will not be
separated. This can be used as:
is( $mock->call_args_string(1), "$mock initialize",
'... passing object, initialize as arguments' );
- "called_ok(method
name, [ test name
])"
Tests to see whether a method of the specified name has been
called on the object. This and the following methods use Test::Builder,
so they integrate nicely with a test suite built around Test::Simple,
Test::More, or anything else compatible:
$mock->foo();
$mock->called_ok( 'foo' );
A generic default test name is provided.
- "called_pos_ok(position,
method name, [ test
name ])"
Tests to see whether the named method was called at the
specified position. A default test name is provided.
- "called_args_pos_is(method
position, argument
position, expected, [
test name ])"
Tests to see whether the argument at the appropriate position
of the method in the specified position equals a specified value. A
default, rather non-descript test name is provided.
- "called_args_string_is(method
position, separator,
expected, [ test
name ])"
Joins together all of the arguments to a method at the
appropriate position and matches against a specified string. A
generically bland test name is provided by default. You can probably do
much better.
- "check_class_loaded( $class_name )"
Attempts to determine whether you have a class of the given
name loaded and compiled. Returns true or false.
Logging
Test::MockObject logs all mocked methods by default. Sometimes you
don't want to do this. To prevent logging all calls to a given method,
prepend the name of the method with "-"
when mocking it.
That is:
$mock->set_true( '-foo', 'bar' );
will set mock both "foo()" and
"bar()", causing both to return true.
However, the object will log only calls to
"bar()", not
"foo()". To log
"foo()" again, merely mock it again
without the leading "-":
$mock->set_true( 'foo' );
$mock will log all subsequent calls to
"foo()" again.
Subclassing
There are two methods provided for subclassing:
- "dispatch_mocked_method( $method_name, @_
)"
This method determines how to call a method (named as
$method_name) not available in this class. It
also controls logging. You may or may not find it useful, but I
certainly take advantage of it for Test::MockObject::Extends.
- "log_call( $method_name, @_ )"
This method tracks the call of the named method and its
arguments.
- Add a factory method to avoid namespace collisions (soon)
- Add more useful methods (catch
"import()"?)
chromatic, <chromatic at wgz dot org>
Thanks go to Curtis 'Ovid' Poe, as well as ONSITE! Technology,
Inc., for finding several bugs and providing several constructive
suggestions.
Jay Bonci also found a false positive in
"called_ok()". Thanks!
Chris Winters was the first to report I'd accidentally scheduled
0.12 for deletion without uploading a newer version. He also gave useful
feedback on Test::MockObject::Extends.
Stevan Little provided the impetus and code for
"set_isa()".
Nicholas Clark found a documentation error.
Mutant suggested a potential problem with
fake_module().
perl, Test::Tutorial, Test::More,
http://www.perl.com/pub/a/2001/12/04/testing.html, and
http://www.perl.com/pub/a/2002/07/10/tmo.html.
Copyright (c) 2002 - 2016 by chromatic <chromatic at wgz dot org>.
This program is free software; you can use, modify, and
redistribute it under the same terms as Perl 5.24 itself.
See http://www.perl.com/perl/misc/Artistic.html
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