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Sam Phippen
How RSpec
Works
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Sam Phippen
@samphippen
Is an RSpec lead
maintainer
And works at
Google
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Sam Phippen
Any code (except code
from RSpec itself) in this
talk is copyright Google
under Apache V2
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Matz Hates Tests
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So RSpec is cancelled
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Sam Phippen
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gem “rspec”, “~> 3.8”
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specs:
diff-lcs (1.3)
rspec (3.8.0)
rspec-core (~> 3.8.0)
rspec-expectations (~> 3.8.0)
rspec-mocks (~> 3.8.0)
rspec-core (3.8.0)
rspec-support (~> 3.8.0)
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rspec
rspec-core
rspec-mocks
rspec-expectations
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rspec
Meta gem that provides the other
gems
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rspec-core
describe, it, runner, let, etc
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rspec-mocks
allow, double, to receive, etc
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rspec-expectations
expect keyword and matchers
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rspec-support
Internal code required to make rspec
work
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gem “rspec-rails”,
“~> 3.8”
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rspec-rails
rspec
rspec-mocks
rspec-core
rspec-expectations
Rails specific
code
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gem “rspec”
gem “rspec-rails”
!
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So, how does RSpec
work?
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RSpec.describe "calculation" do
it "can add numbers" do
expect(1 + 1).to eq(2)
end
end
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RSpec.describe "calculation" do
it "can add numbers" do
expect(1 + 1).to eq(2)
end
end
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Example Group
l/r-c/
example_group.rb
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bundle exec rspec
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Runner
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World
Runner
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l/r-c/runner.rb
l/r-c/world.rb
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—pattern=spec/**/*_spec.rb
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World
Runner
ExampleGroup
ExampleGroup
ExampleGroup
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—tag=foo
(e.g describe, “…”, :foo do)
—example=“calculates 4+4”
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Runner
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Runner
Configuration
Options
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Runner
Configuration
Options
FilterManager
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World
ExampleGroup
ExampleGroup
ExampleGroup
FilterManager
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World
ExampleGroup
ExampleGroup
ExampleGroup
FilterManager
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World contains many
ExampleGroups ready
for execution
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RSpec.describe "calculation" do
it "can add numbers" do
expect(1 + 1).to eq(2)
end
end
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Example
l/r-c/
example.rb
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A “test”
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RSpec.describe "eg1" do
it "e1"
it "e2"
context "eg1_1" do
it "e3"
end
context "eg2_1" do
it "e3"
end
end
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EG EG
E E EG
E E
E E
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So what about
randomization?
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E
EG E EG
EG
E E
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RSpec.describe "eg1" do
before {}
after {}
around { |ex| ex.run}
it "e1"
end
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RSpec.describe "eg1" do
before {}
after {}
around { |ex| ex.run}
it "e1"
end
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Hooks
l/r-c/
hooks.rb
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Execute once
before(:suite)
after(:suite)
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Execute once per
example group
before(:context)
after(:context)
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Execute once per
example
before
after
around
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EG E
BS BC B E
B
A A
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EG E
BC B
A AC
B
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RSpec core is only
responsible for the structure
and execution of your test
suite
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RSpec.describe "calculation" do
it "can add numbers" do
expect(1 + 1).to eq(2)
end
end
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Expectation
Provided by
rspec-expectations
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RSpec.describe "calculation" do
it "can add numbers" do
expect(1 + 1).to eq(2)
end
end
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ExpectationTarget
Matcher
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ExpectationTarget
Matcher
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expect(…).to
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def to(matcher=nil, message=nil, &block)
RSpec::Expectations::
PositiveExpectationHandler
.handle_matcher(target, matcher,
message, &block)
end
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expect(…).to_not
expect(…).not_to
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def not_to(matcher=nil, message=nil,
&block)
RSpec::Expectations::
NegativeExpectationHandler
.handle_matcher(target, matcher,
message, &block)
end
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ExpectationTarget wraps a
user object for matching
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RSpec.describe "calculation" do
it "can add numbers" do
expect(1 + 1).to eq(2)
end
end
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ExpectationTarget
Matcher
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def eq(expected)
BuiltIn::Eq
.new(expected)
end
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class Eq < BaseMatcher
def match(expected, actual)
actual == expected
end
end
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class BaseMatcher
include RSpec::Matchers::Composable
def matches?(actual)
@actual = actual
match(expected, actual)
end
end
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RSpec.describe "calculation" do
it "can add numbers" do
expect(1 + 1).to eq(2)
end
end
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Composable
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expect(…).to match([
a_kind_of(String),
a_hash_including(a: 4)
])
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[
“any string”,
{a: 4, b: 6.0},
]
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class Match < BaseMatcher
def match(expected, actual)
return true if values_match?(
expected, actual)
actual.match(expected)
end
end
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class Match < BaseMatcher
def match(expected, actual)
return true if values_match?(
expected, actual)
actual.match(expected)
end
end
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def values_match?(expected, actual)
expected =
with_matchers_cloned(expected)
Support::FuzzyMatcher.values_match?(
expected, actual)
end
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RSpec support is shared
code between RSpec
libraries
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def self.values_match?(expected, actual)
if Hash === actual
return hashes_match?(expected, actual) if Hash === expected
elsif Array === expected
&& Enumerable === actual
&& !(Struct === actual)
return arrays_match?(expected, actual.to_a)
end
return true if expected == actual
begin
expected === actual
rescue ArgumentError
# Some objects, like 0-arg lambdas on 1.9+, raise
# ArgumentError for `expected === actual`.
false
end
end
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You can’t read this.
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def self.values_match?(e, a)
if Hash === a
return hashes_match?(e, a) if Hash
=== e
elsif Array === e
&& Enumerable === a
&& !(Struct === a)
return arrays_match?(
e, a)
end
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def self.values_match?(e, a)
if Hash === a
return hashes_match?(e, a) if Hash
=== e
elsif Array === e
&& Enumerable === a
&& !(Struct === a)
return arrays_match?(
e, a)
end
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def self.hashes_match?(
expected_hash, actual_hash)
return false if
expected_hash.size != actual_hash.size
expected_hash.all? do |e_k, e_v|
actual_value = actual_hash.fetch(e_k) {
return false }
values_match?(e_v, actual_value)
end
end
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def self.hashes_match?(
expected_hash, actual_hash)
return false if
expected_hash.size != actual_hash.size
expected_hash.all? do |e_k, e_v|
actual_value = actual_hash.fetch(e_k) {
return false }
values_match?(e_v, actual_value)
end
end
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def self.hashes_match?(
expected_hash, actual_hash)
return false if
expected_hash.size != actual_hash.size
expected_hash.all? do |e_k, e_v|
actual_value = actual_hash.fetch(e_k) {
return false }
values_match?(e_v, actual_value)
end
end
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def self.hashes_match?(
expected_hash, actual_hash)
return false if
expected_hash.size != actual_hash.size
expected_hash.all? do |e_k, e_v|
actual_value = actual_hash.fetch(e_k) {
return false }
values_match?(e_v, actual_value)
end
end
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def self.hashes_match?(
expected_hash, actual_hash)
return false if
expected_hash.size != actual_hash.size
expected_hash.all? do |e_k, e_v|
actual_value = actual_hash.fetch(e_k) {
return false }
values_match?(e_v, actual_value)
end
end
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def self.values_match?(e, a)
if Hash === a
return hashes_match?(e, a) if Hash
=== e
elsif Array === e
&& Enumerable === a
&& !(Struct === a)
return arrays_match?(
e, a)
end
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def self.arrays_match?(
expected_list, actual_list)
return false if
expected_list.size!=actual_list.size
expected_list.zip(actual_list).all? do
|expected, actual|
values_match?(expected, actual)
end
end
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def self.arrays_match?(
expected_list, actual_list)
return false if
expected_list.size!=actual_list.size
expected_list.zip(actual_list).all? do
|expected, actual|
values_match?(expected, actual)
end
end
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def self.arrays_match?(
expected_list, actual_list)
return false if
expected_list.size!=actual_list.size
expected_list.zip(actual_list).all? do
|expected, actual|
values_match?(expected, actual)
end
end
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RSpec recurses array and
hash data structures,
doing matches.
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def values_match(expected, actual)
… (the code we saw earlier)
return true if expected == actual
begin
expected === actual
rescue ArgumentError
# Some objects, like 0-arg lambdas on
# 1.9+, raise
# ArgumentError for `expected === actual`.
false
end
end
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def values_match(expected, actual)
… (the code we saw earlier)
return true if expected == actual
begin
expected === actual
rescue ArgumentError
# Some objects, like 0-arg lambdas on
# 1.9+, raise
# ArgumentError for `expected === actual`.
false
end
end
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def values_match(expected, actual)
… (the code we saw earlier)
return true if expected == actual
begin
expected === actual
rescue ArgumentError
# Some objects, like 0-arg lambdas on
# 1.9+, raise
# ArgumentError for `expected === actual`.
false
end
end
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/a/ === “a”
lambda { |x| x == 1 } === 1
Any Rspec matcher === a value it matches
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RSpec aliases === to
matches? On matchers
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So let’s put it all back
together
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expect(…).to match([
a_kind_of(String),
a_hash_including(a: 4)
])
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[
“any string”,
{a: 4, b: 6.0},
]
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Call arrays_match?
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[
“any string”,
{a: 4, b: 6.0},
]
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Call === on
“a_kind_of(String)”
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[
“any string”, ✅
{a: 4, b: 6.0},
]
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Call === on
a_hash_including?(a: 4)
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[
“any string”, ✅
{a: 4, b: 6.0}, ✅
]
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Match returns true
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RSpec expectations
contains expect, and
matching logic.
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rspec-mocks
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RSpec.describe "mocking" do
it “adds a foo method" do
allow(foo).to
receive(:bees)
expect(foo.bees).to eq(nil)
end
end
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RSpec.describe "mocking" do
it “adds a foo method" do
allow(foo).to
receive(:bees)
expect(foo.bees).to eq(nil)
end
end
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AllowanceTarget
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AllowanceTarget
TargetBase
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AllowanceTarget
calls #delegate_to
with :setup_allowance
on TargetBase
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expect(foo).to
receive
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ExpectationTarget
calls #delegate_to
with :setup_expectation
on TargetBase
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AllowanceTarget
TargetBase
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TargetBase
defines #to
on AllowanceTarget
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The defined #to
calls :setup_allowance
on matchers passed to
#to
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This meta programming
step allows deduplication
with ExpectationTarget
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AllowanceTarget
TargetBase
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RSpec.describe "mocking" do
it “adds a foo method" do
allow(foo).to
receive(:bees)
expect(foo.bees).to eq(nil)
end
end
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Receive
matcher handles stubbing
and mocking for RSpec
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AllowanceTarget#to
calls setup_allowance
on the passed matcher
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AllowanceTarget
TargetBase
Receive
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Receive#setup_allowance
creates a Proxy for object
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AllowanceTarget
TargetBase
Receive
Proxy
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Receive#setup_allowance
Calls #add_stub on the
Proxy
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Proxy manages all mocks
and stubs for an object
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Proxy#add_stub creates
a MethodDouble for the
stubbed method
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AllowanceTarget
TargetBase
Receive
Proxy
Method double
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MethodDouble saves
the original
implementation
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MethodDouble creates
the stub implementation
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RSpec.describe "mocking" do
it “adds a foo method" do
allow(foo).to
receive(:bees)
expect(foo.bees).to eq(nil)
end
end
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Calling foo.bees calls the
stubbed implementation
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Call foo.bees
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Method double
Call foo.bees
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Proxy
Method double
Call foo.bees
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Invoke stub Proxy
Method double
Call foo.bees
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Invoke stub
Return value
Proxy
Method double
Call foo.bees
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RSpec.describe "mocking" do
it “adds a foo method" do
allow(foo).to
receive(:bees)
expect(foo.bees).to eq(nil)
end
end
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At the end of the test, the
MethodDouble puts the
original method back on
the object
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And that’s stubs
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RSpec.describe "mocking" do
it “adds a foo method" do
expect(foo).to
receive(:bees)
expect(foo.bees).to eq(nil)
end
end
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ExpectationTarget
TargetBase
Receive
Proxy
Method double
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At the end of each test,
RSpec invokes
RSpec::Mocks.verify
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RSpec::Mocks.verify
enumerates all
MethodDoubles
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MethodDoubles raise if
their conditions weren’t
met
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RSpec mocks has a lot
more power, this is a
high level overview
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rspec-core
describe, it, runner, let, etc
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rspec-expectations
expect keyword and matchers
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rspec-mocks
allow, double, to receive, etc