Fixtures
A fixture is a pre-defined, reusable test abstraction. The objects under test are specified at runtime, rather than hard-coded.
To get a better understanding of fixtures, imagine a regular test file, but the object (or objects) under test can be swapped so that the same standardized test implementation can be used against multiple objects.
A fixture is just a plain old Ruby object that includes the TestBench API. A fixture has access to the same API that any TestBench test would. By including the TestBench::Fixture
module into a Ruby object, the object acquires all of the methods available to a test script, including context
, test
, assert
, refute
, assert_raises
, refute_raises
, comment
, and detail
.
Fixture API
Callable Object
The only requirement placed on a fixture's API is that it implements Ruby's callable object protocol by implementing the call
method, and that the signature of the method is parameterless.
Alternatively, if the call
method is not implemented on a fixture, then a block must be given. When a block is given, the fixture object doesn't have to implement the callable object protocol. If call
is implemented and a block is given, the block has precedence.
Fixture State and the Initializer
State is passed to a fixture object via the positional parameters of its initializer.
class SomeFixture
include TestBench::Fixture
def initialize(something, something_else)
@something = something
@something_else = something_else
end
def call
# ...
end
end
If the fixture class implements a method named build
, that method will be used to construct an instance rather than the initializer, leaving the developer the freedom to either implement the initialize
method or not, or implement it whatever is preferred.
Implementing Fixtures
The TestBench API is just Ruby methods. There's no special syntax to invoke TestBench API methods, or any special rules or setup.
In the simplest case, a test can be implemented directly in the call
method.
class SomeFixture
include TestBench::Fixture
attr_accessor :something
attr_accessor :something_else
def initialize(something, something_else)
@something = something
@something_else = something_else
end
def call
context "Some Context" do
context "Something" do
included = something_else.include?(something)
test "Included in Something Else" do
assert(included)
end
end
context "Something Else" do
twice_as_long = something_else.length == something.length * 2
test "Twice as long as something" do
assert(twice_as_long)
end
end
end
end
end
Object Extension
Objects can be dispositioned as fixtures at runtime by having a module named Fixture
within their class's namespace. TestBench will extend both the Fixture
module and TestBench::Fixture
onto the object:
class SomeClass
attr_accessor :some_attr
module Fixture
def assert_some_attr
test "Some test" do
assert(!!some_attr)
end
end
end
end
Using Fixtures
In addition to TestBench's core API for writing tests, the API also provides the fixture
method for activating fixtures in a test script.
context "Some Fixture" do
something = 'some value'
something_else = something * 2
fixture(SomeFixture, something, something_else)
end
The fixture
method runs the test code in the fixture as if it's part of the currently running test, maintaining the continuity of the output and indenting.
Other Context
Some Context
Something
Included in Something Else
Something Else
Twice as long as something
In addition to class fixtures, fixture
accepts objects that include a module named Fixture
within their class's namespace:
context "Some Object Fixture" do
object = SomeClass.new
fixture(object) do
object.assert_some_attr
end
end
API
fixture(fixture_class_or_object, *args, &block)
Parameters
Name | Description | Type |
---|---|---|
fixture_class_or_object | Fixture class or object that will be actuated | Class, Object |
args | Arguments to pass to a fixture class's initializer | Array |
block | Additional test code that is executed within the fixture's context | Proc |
When supplied a fixture class, the fixture
method instantiates the fixture class and invokes it's call
method. The parameters sent to the fixture
method are passed along to the fixture's initializer.
When supplied a fixture object, the fixture
method extends TestBench::Fixture
onto the object as well as the object's Fixture
module. If no Fixture
module can be resolved, an error is raised.
The fixture
method also shares the running test script's output object with the fixture in order to preserve output continuity.
Additional Block
When the generalization provided by a fixture is not enough, the fixture can be specialized for a particular circumstance by supplying an additional block of test code.
When a block is given, the fixture object doesn't have to implement the callable object protocol.
context "Other Context" do
something = 'some value'
something_else = 'some value' * 2
fixture(SomeFixture, something, something_else) do |f|
context "Something Else" do
context "First Character" do
first_character = f.something_else[0]
last_character = f.something_else[-1]
same = first_character == last_character
test "Not the same as the last character" do
refute(same)
end
end
end
end
end
Other Context
Some Context
Something
Included in Something Else
Something Else
Twice as long as something
Something Else
First Character
Not the same as the last character
Exercising Fixtures
Because fixtures are just Ruby objects, they can be instantiated and exercised just like any other Ruby object.
something = 'some value'
something_else = 'some value'
some_fixture = SomeFixture.new(something, something_else)
some_fixture.()
puts TestBench::Fixture.output(some_fixture)
Some Context
Something
Included in Something Else
Something Else
Twice as long as something
Assertion failed
Failure: 1
Testing Fixtures
If a fixture is sufficiently elaborate, it can even be tested like a plain old object.
context "SomeFixture" do
something = 'some value'
something_else = 'some value'
some_fixture = SomeFixture.new(something, something_else)
some_fixture.()
context "Included in Something Else" do
passed = some_fixture.test_session.test_passed?('Included in Something Else')
test "Passed" do
assert(passed)
end
end
context "Twice as long as something" do
failed = some_fixture.test_session.test_failed?('Twice as long as something')
test "Failed" do
assert(failed)
end
end
end
SomeFixture
Included in Something Else
Passed
Twice as long as something
Failed
Distributing Fixtures with a Library
Libraries can provide a set of fixtures that users of the library can leverage to test code that uses the library.
A library that ships a set of fixtures doesn't have to take a dependency on the entirety of TestBench. The TestBench::Fixture
namespace is its own self-contained package. That package is safe to be packaged with production code, whereas TestBench, being a test framework, should not be distributed with production code.