module Spec

Overview

Crystal's built-in testing library. It provides a structure for writing executable examples of how your code should behave. A domain specific language allows you to write them in a way similar to natural language.

The Crystal compiler has aspec command with tools to constrain which examples get run and tailor the output.

A basic spec looks something like this:

require "spec"

describe Array do
  describe "#size" do
    it "correctly reports the number of elements in the Array" do
      [1, 2, 3].size.should eq 3
    end
  end

  describe "#empty?" do
    it "is empty when no elements are in the array" do
      ([] of Int32).empty?.should be_true
    end

    it "is not empty if there are elements in the array" do
      [1].empty?.should be_false
    end
  end

  # lots more specs
end

Test files are structured by use of thedescribe orcontext methods. Typically a top leveldescribe defines theouter unit (such as a class) that is to be tested by the spec. Furtherdescribe calls can be nested within the outer unit to specify smaller units under test (such as individual methods). describe can also be used to set up a certain context - think emptyArray versus Array with elements. Thecontext method behaves just like thedescribe method and may be used instead, to emphasize context to the reader.

Within adescribe block, concrete test cases are defined withit . A descriptive string is supplied toit describing what the test case tests specifically.

Specs then use theshould method to verify that the expected value is returned. See the example above for details.

By convention, specs live in thespec directory of a project. You can compile and run the specs of a project by runningcrystal spec.

# Run all specs in files matching spec/**/*_spec.cr
crystal spec

# Run all specs in files matching spec/my/test/**/*_spec.cr
crystal spec spec/my/test/

# Run all specs in spec/my/test/file_spec.cr
crystal spec spec/my/test/file_spec.cr

# Run the spec or group defined in line 14 of spec/my/test/file_spec.cr
crystal spec spec/my/test/file_spec.cr:14

# Run all specs tagged with "fast"
crystal spec --tag 'fast'

# Run all specs not tagged with "slow"
crystal spec --tag '~slow'

Focusing on a group of specs

Adescribe,context orit can be marked withfocus: true, like this:

it "adds", focus: true do
  (2 + 2).should_not eq(5)
end

If any such thing is marked withfocus: true then only those examples will run.

Randomizing order of specs

Specs, by default, run in the order defined, but can be run in a random order by passing--order random tocrystal spec.

Specs run in random order will display a seed value upon completion. This seed value can be used to rerun the specs in that same order by passing the seed value to--order.

Defined in:

Class Method Summary

• .add_formatter(formatter)

  DEPRECATED This is an internal API.

• .add_split_filter(filter)

  DEPRECATED This is an internal API.

• .after_each(&block)

  Instructs the spec runner to execute the given block after each spec in the spec suite.

• .after_suite(&block)

  Instructs the spec runner to execute the given block after the entire spec suite.

• .around_each(&block : Example::Procsy -> )

  Instructs the spec runner to execute the given block when each spec in the spec suite runs.

• .before_each(&block)

  Instructs the spec runner to execute the given block before each spec in the spec suite.

• .before_suite(&block)

  Instructs the spec runner to execute the given block before the entire spec suite.

• .finish_run

  DEPRECATED This is an internal API.

• .override_default_formatter(formatter)

  DEPRECATED This is an internal API.

• .randomizer : Random::PCG32 | Nil

  DEPRECATED This is an internal API.

Class Method Detail

Spec.after_each { puts 1 }
Spec.after_each { puts 2 }

Spec.after_suite { puts 1 }
Spec.after_suite { puts 2 }

require "spec"

Spec.around_each do |example|
  puts "runs before each sample"
  example.run
  puts "runs after each sample"
end

it { }
it { }

Spec.before_each { puts 1 }
Spec.before_each { puts 2 }

Spec.before_suite { puts 1 }
Spec.before_suite { puts 2 }