Shared Examples

Transcript

1. Shared Examples 1
2. What are Shared Examples? Shared examples are used to to create reusable test examples. They are often used to: • DRY up tests • Enforce an interface 2
3. Feature Request #1 class RevenueByLocationReport def description "Revenue for each location" end def headers ["Location", "Revenue"] end end 3
4. Feature Request #1 - Tests RSpec.describe RevenueByLocationReport do describe "#description" do it "returns a description of the reports purpose" do report = RevenueByLocationReport.new description = report.description expect(description).to eq("Revenue for each location") end end describe "#headers" do it "returns descriptive headers" do report = RevenueByLocationReport.new headers = report.headers expect(headers).to eq(["Location", "Revenue"]) end end end 4
5. Feature Request #2 class RevenueByProjectReport def description "Revenue for each project" end def headers ["Project", "Location", "Revenue"] end end 5
6. Feature Request #2 - Tests RSpec.describe RevenueByProjectReport do describe "#description" do it "returns a description of the reports purpose" do report = RevenueByProjectReport.new description = report.description expect(description).to eq("Revenue for each project") end end describe "#headers" do it "returns descriptive headers" do report = RevenueByProjectReport.new headers = report.headers expect(headers).to eq(["Project", "Location", "Revenue"]) end end end 6
7. Similar Test Examples RSpec.describe RevenueByLocationReport do describe "#description" do it "returns a description of the reports purpose" do # verify the description end end describe "#headers" do it "returns descriptive headers" do # verify the headers end end end RSpec.describe RevenueByProjectReport do describe "#description" do it "returns a description of the reports purpose" do # verify the description end end describe "#headers" do it "returns descriptive headers" do # verify the headers end end end 7
8. Defining a Shared Example # spec/shared_examples/report_examples.rb RSpec.shared_examples "a report" do describe "#description" do it "returns a String describing the reports purpose" do report = described_class.new expect(report.description).to be_a String end end describe "#headers" do it "returns an Array of descriptive headers" do report = described_class.new expect(report.headers).to be_an Array expect(report.headers).to be_present end end end 8
9. described_class - Given a Class RSpec.describe User do describe "described_class" do it "references the class being described" do puts described_class # => User puts described_class.new # => #<User:0x00007fe605872510> expect(described_class).to eq(User) # => true end end end When a class name is passed to describe, the class is available via the described_class method. 9
10. described_class - Given a String RSpec.describe "User" do describe "described_class" do it "references the described class" do described_class.new # => error: undefined method on nil puts described_class.class # => NilClass end end end When a string is passed to describe, described_class is nil. 10
11. Implicit Subject RSpec.describe Array do describe "implicit subject" do context "given a class" do it "sets the subject to an instance of the class" do puts subject.inspect #=> [] expect(subject).to be_empty end end end end When a Class is passed to describe, an instance of the Class is available via subject 11
12. Implicit Subject RSpec team recommendation: • Reserve the use of subject for custom matchers 12
13. Explicit Subject RSpec.describe Array do subject { [1,2,3] } describe "explicit subject" do it "sets the subject to an instance of the class" do expect(subject).to eq([1,2,3]) end end end You can override the implicit subject by explicitly setting the subject. 13
14. RSpec Subject vs Let Subject • memoized helper • Set by RSpec (or the test author) • Lazy-evaluated • Used for one-line syntax * • Used for custom matchers # * Example of one-line syntax: RSpec.describe Array do it { is_expected.to eq([]) } # is_expected calls expect(subject).to eq([]) end Let • memoized helper • Set by the test author • Lazy-evaluated • used to reduce duplication • used to create state that is reset between each example 14
15. Report Shared Examples # spec/shared_examples/report_examples.rb RSpec.shared_examples "a report" do describe "description" do it "returns a String describing the reports purpose" do report = described_class.new expect(report.description).to be_a String end end describe "headers" do it "returns an Array of descriptive headers" do report = described_class.new expect(report.headers).to be_an Array expect(report.headers).to be_present end end end 15
16. Defining a Shared Example - Refactor # spec/shared_examples/report_examples.rb RSpec.shared_examples "a report" do let(:report) { described_class.new } describe "description" do it "returns a String describing the reports purpose" do expect(report.description).to be_a String end end describe "headers" do it "returns an Array of descriptive headers" do expect(report.headers).to be_an Array expect(report.headers).to be_present end end end 16
17. Revisit the Tests RSpec.describe RevenueByLocationReport do describe "description" do it "returns a description of the reports purpose" do # verify the description end end describe "headers" do it "returns descriptive headers" do # verify the headers end end end RSpec.describe RevenueByProjectReport do describe "description" do it "returns a description of the reports purpose" do # verify the description end end describe "headers" do it "returns descriptive headers" do # verify the headers end end end 17
18. Use the Shared Example RSpec.describe RevenueByLocationReport do it_behaves_like "a report" end RSpec.describe RevenueByProjectReport do it_behaves_like "a report" end 18
19. Calling a Shared Example include_examples "a report" (includes the example in the current context) # RevenueByLocationReport # description # returns a String describing the reports purpose it_behaves_like "a report" (includes the example in a nested context) # RevenueByLocationReport # behaves like a report # description # returns a String describing the reports purpose it_should_behave_like "a report" (includes the example in a nested context) # RevenueByLocationReport # it should behave like a report # description # returns a String describing the reports purpose 19
20. Enforce an interface Shared examples are used to to create reusable test examples. They are often used to: • DRY up tests • Enforce an interface 20
21. Enforce an interface class Product include MarkdownDescription end class Location include MarkdownDescription end 21
22. Enforce an interface module MarkdownDescription MARKDOWN_TEMPLATE = "string://<div class='markdown'><%= @body %></div>" def description_html Kramdown::Document.new( process_pasted_content, template: MARKDOWN_TEMPLATE, ).to_html end private HEADER_MATCH = /\n\n([A-Z &]+:)\n/ HEADER_MARKDOWN = "\n\n\\1\n\n".freeze LIST_MATCH = /\n(?:•|\*)/ LIST_MARKDOWN = "\n* ".freeze def process_pasted_content description.to_s. gsub(HEADER_MATCH, HEADER_MARKDOWN). gsub(LIST_MATCH, LIST_MARKDOWN) end end 22
23. Define a Shared Example RSpec.shared_examples "a record with markdown description" do describe "#description_html" do it "method exists" do record = described_class.new expect(record).to respond_to(:description_html) end end end 23
24. Enforce an interface - Tests RSpec.describe Product do it_behaves_like "a record with a markdown description" end RSpec.describe Location do it_behaves_like "a record with a markdown description" end 24
25. Shared Examples Review • Help us reuse common test examples by extracting test examples to a shared location • Use shared examples sparingly as they increase indirection • Shared Examples are highly general and portable • Store shared examples within a spec/support/ shared_examples/ directory (example: /spec/shared_examples/shared_example.rb) 25
26. shared_context vs shared_examples shared_context is an alias for shared_examples shared_example is used to extract a test example shared_context is used to extract test setup 26
27. Resources RSpec Shared Examples - https://relishapp.com/rspec/rspec- core/docs/example-groups/shared- examples RSpec shared_context - https://github.com/rspec/rspec-core/ blob/ 922b4a6dc5ca397df19f5f282f2f6a2465b 2e24a/lib/rspec/core/ shared_example_group.rb#L100 27