Managing `let`

Dive into RSpec's `let`, how it works, and best practices.

Transcript

1. Managing let 1
2. lets recap • defines memoized helper method • is lazy-evaluated (unless you let!) • is caches across multiple calls • is not cached across examples 2
3. lets recap # let_spec.rb RSpec.describe "let" do let(:user) { FactoryBot.build_stubbed(:user, name: "Josh") } it "does not instantiate immediately" do # user has not been created yet expect(true).to be_true end it "memoizes the value" do user.update(name: "Stephanie") expect(user.name).to eq("Stephanie") expect(user.name).to eq("Stephanie") end it "does not cache across examples" do expect(user.name).to eq("Josh") end end 3
4. lets see the benefits • DRYs up our code * • Avoids building extra data * • Makes tests easier to read * RSpec.describe "user" do let(:user) { FactoryBot.build_stubbed(:user, birthdate: 366.days.ago)} describe "#age" do it "calculates age given birthdate" do expect(user.age).to eq(1) end end describe "#birthday" do it "displays the month and day" do expect(user.birthday).to eq("October 28") end end end 4
5. DRY-s up our code* 5
6. "Code so dry it chafes" 6
7. describe "#age" do it "calcuates age given birthdate" do expect(user.age).to eq(1) end end 7
8. Avoids building extra data * 8
9. RSpec.describe "User" do let(:org) { FactoryBot.build_stubbed(:organization, name: "AB Inc")} let(:user) { FactoryBot.build_stubbed(:user, role: "CEO", birthdate: 366.days.ago, organization: org)} describe "#age" do it "calculates age given birthdate" do expect(user.age).to eq(1) end end describe "#birthday" do it "displays the month and day" do expect(user.birthday).to eq("October 28") end end describe "#title" do it "returns the title and company" do expect(user.title).to eq("CEO at AB Inc") end end end 9
10. Makes tests easier to read* 10
11. Where is created_ng coming from? 11
12. Where is created_ng coming from? The top of the file: 12
13. lets talk about scope 13
14. # scope_spec.rb RSpec.describe "scope" do let(:favorite_number) { 5 } it "uses the top scoped value" do expect(favorite_number).to eq(5) end describe "within a more specific scope" do let(:favorite_number) { 12 } it "uses the more specific value" do expect(favorite_number).to eq(12) end context "when the number is 3" do let(:favorite_number) { 3 } it "returns 3" do expect(favorite_number).to eq(3) end end end it "uses relative scope" do expect(favorite_number).to eq(5) end end 14
15. # scope_spec.rb RSpec.describe "scope" do let(:favorite_number) { 5 } it "uses the top scoped value" do expect(favorite_number).to eq(5) end describe "within a more specific scope" do let(:favorite_number) { 12 } it "uses the more specific value" do expect(favorite_number).to eq(12) end context "when the number is 3" do let(:favorite_number) { 3 } it "returns 3" do expect(favorite_number).to eq(3) end end end it "uses relative scope" do expect(favorite_number).to eq(5) end end 15
16. # scope_spec.rb RSpec.describe "scope" do let(:favorite_number) { 5 } it "uses the top scoped value" do expect(favorite_number).to eq(5) end describe "within a more specific scope" do let(:favorite_number) { 12 } it "uses the more specific value" do expect(favorite_number).to eq(12) end context "when the number is 3" do let(:favorite_number) { 3 } it "returns 3" do expect(favorite_number).to eq(3) end end end it "uses relative scope" do expect(favorite_number).to eq(5) end end 16
17. # scope_spec.rb RSpec.describe "scope" do let(:favorite_number) { 5 } it "uses the top scoped value" do expect(favorite_number).to eq(5) end describe "within a more specific scope" do let(:favorite_number) { 12 } it "uses the more specific value" do expect(favorite_number).to eq(12) end context "when the number is 3" do let(:favorite_number) { 3 } it "returns 3" do expect(favorite_number).to eq(3) end end end it "uses relative scope" do expect(favorite_number).to eq(5) end end 17
18. # scope_spec.rb RSpec.describe "scope" do let(:favorite_number) { 5 } it "uses the top scoped value" do expect(favorite_number).to eq(5) end describe "within a more specific scope" do let(:favorite_number) { 12 } it "uses the more specific value" do expect(favorite_number).to eq(12) end context "when the number is 3" do let(:favorite_number) { 3 } it "returns 3" do expect(favorite_number).to eq(3) end end end it "uses relative scope" do expect(favorite_number).to eq(5) end end 18
19. lets move forward 19
20. let's not RSpec.describe "User" do describe "#age" do it "calculates age given birthdate" do user = FactoryBot.build_stubbed(:user, birthdate: 366.days.ago) expect(user.age).to eq(1) end end describe "#birthday" do it "displays the month and day" do user = FactoryBot.build_stubbed(:user, birthdate: 366.days.ago) expect(user.birthday).to eq("October 28") end end describe "#title" do it "displays the title and company" do org = FactoryBot.build_stubbed(:organization, name: "AB Inc") user = FactoryBot.build_stubbed(:user, role: "CEO", birthdate: 366.days.ago, organization: org) expect(user.title).to eq("CEO at AB Inc") end end end 20
21. lets do RSpec.describe "User" do let(:user) { FactoryBot.build_stubbed(:user, birthdate: birthdate) } describe "#age" do let(:birthdate) { 366.days.ago } it "calculates age given birthdate" do expect(user.age).to eq(1) end end describe "#birthday" do let(:birthdate) { 366.days.ago } it "displays the month and day" do expect(user.birthday).to eq("October 28") end end describe "#title" do let(:user) { FactoryBot.build_stubbed(:user, role: "CEO", organization: org) } let(:org) { FactoryBot.build_stubbed(:org, name: "AB Inc") } it "displays the title and company" do expect(user.title).to eq("CEO at AB Inc") end end end 21
22. lets do RSpec.describe "User" do let(:user) { FactoryBot.build_stubbed(:user, birthdate: birthdate) } describe "#age" do let(:birthdate) { 366.days.ago } it "calculates age given birthdate" do expect(user.age).to eq(1) end end describe "#birthday" do let(:birthdate) { 366.days.ago } it "displays the month and day" do expect(user.birthday).to eq("October 28") end end describe "#title" do let(:user) { FactoryBot.build_stubbed(:user, role: "CEO", organization: org) } let(:org) { FactoryBot.build_stubbed(:org, name: "AB Inc") } it "displays the title and company" do expect(user.title).to eq("CEO at AB Inc") end end end 22
23. lets do RSpec.describe "User" do let(:user) { FactoryBot.build_stubbed(:user, birthdate: birthdate) } describe "#age" do let(:birthdate) { 366.days.ago } it "calculates age given birthdate" do expect(user.age).to eq(1) end end describe "#birthday" do let(:birthdate) { 366.days.ago } it "displays the month and day" do expect(user.birthday).to eq("October 28") end end describe "#title" do let(:user) { FactoryBot.build_stubbed(:user, role: "CEO", organization: org) } let(:org) { FactoryBot.build_stubbed(:org, name: "AB Inc") } it "displays the title and company" do expect(user.title).to eq("CEO at AB Inc") end end end 23
24. lets do RSpec.describe "User" do let(:user) { FactoryBot.build_stubbed(:user, birthdate: birthdate) } describe "#age" do let(:birthdate) { 366.days.ago } it "calculates age given birthdate" do expect(user.age).to eq(1) end end describe "#birthday" do let(:birthdate) { 366.days.ago } it "displays the month and day" do expect(user.birthday).to eq("October 28") end end describe "#title" do let(:user) { FactoryBot.build_stubbed(:user, role: "CEO", organization: org) } let(:org) { FactoryBot.build_stubbed(:org, name: "AB Inc") } it "displays the title and company" do expect(user.title).to eq("CEO at AB Inc") end end end 24
25. Prioritize readability 25
26. Avoid deeply nested scopes 26
27. Consider refactoring long files 27
28. Don't reassign variables in a let 28
29. RSpec.describe "user" do let(:user) { FactoryBot.build_stubbed(:user, birthdate: 365.days.ago)} describe "#age" do context "when the user is exactly one year old" do it "calculates age given birthdate" do expect(user.age).to eq(1) end end context "when they are less than six months towards their next year" do let(:user) { FactoryBot.build_stubbed(:user, birthdate: 385.days.ago)} it "rounds down" do expect(user.age).to eq(1) end end end end 29
30. RSpec.describe "user" do let(:user) { FactoryBot.build_stubbed(:user, birthdate: 365.days.ago)} describe "#age" do context "when the user is exactly one year old" do it "calculates age given birthdate" do expect(user.age).to eq(1) end end context "when they are less than six months towards their next year" do let(:user) { FactoryBot.build_stubbed(:user, birthdate: 385.days.ago)} it "rounds down" do expect(user.age).to eq(1) end end end end 30
31. RSpec.describe "user" do let(:user) { FactoryBot.build_stubbed(:user, birthdate: 365.days.ago)} describe "#age" do context "when the user is exactly one year old" do it "calculates age given birthdate" do expect(user.age).to eq(1) end end context "when they are less than six months towards their next year" do let(:user) { FactoryBot.build_stubbed(:user, birthdate: 385.days.ago)} it "rounds down" do expect(user.age).to eq(1) end end end end 31
32. RSpec.describe "user" do let(:user) { FactoryBot.build_stubbed(:user, birthdate: 365.days.ago)} describe "#age" do context "when the user is exactly one year old" do it "calculates age given birthdate" do expect(user.age).to eq(1) end end context "when they are less than six months towards their next year" do let(:user) { FactoryBot.build_stubbed(:user, birthdate: 385.days.ago)} it "rounds down" do expect(user.age).to eq(1) end end end end 32
33. RSpec.describe "user" do let(:user) { FactoryBot.build_stubbed(:user, birthdate: birthdate)} describe "#age" do context "when the user is exactly one year old" do let(:birthdate) { 365.days.ago } it "calculates age given birthdate" do expect(user.age).to eq(1) end end context "when they are less than six months towards their next year" do let(:birthdate) { 385.days.ago } it "rounds down" do expect(user.age).to eq(1) end end end end 33
34. RSpec.describe "user" do let(:user) { FactoryBot.build_stubbed(:user, birthdate: birthdate)} describe "#age" do context "when the user is exactly one year old" do let(:birthdate) { 365.days.ago } it "calculates age given birthdate" do expect(user.age).to eq(1) end end context "when they are less than six months towards their next year" do let(:birthdate) { 385.days.ago } it "rounds down" do expect(user.age).to eq(1) end end end end 34
35. RSpec.describe "user" do let(:user) { FactoryBot.build_stubbed(:user, birthdate: birthdate)} describe "#age" do context "when the user is exactly one year old" do let(:birthdate) { 365.days.ago } it "calculates age given birthdate" do expect(user.age).to eq(1) end end context "when they are less than six months towards their next year" do let(:birthdate) { 385.days.ago } it "rounds down" do expect(user.age).to eq(1) end end end end 35
36. RSpec.describe "user" do let(:user) { FactoryBot.build_stubbed(:user, birthdate: birthdate)} describe "#age" do context "when the user is exactly one year old" do let(:birthdate) { 365.days.ago } it "calculates age given birthdate" do expect(user.age).to eq(1) end end context "when they are less than six months towards their next year" do let(:birthdate) { 385.days.ago } it "rounds down" do expect(user.age).to eq(1) end end end end 36
37. Resources My issues with let - https://thoughtbot.com/blog/my-issues-with-let Let's not - https://thoughtbot.com/blog/lets-not Mystery guest - https://thoughtbot.com/blog/mystery-guest The self-contained test - https://thoughtbot.com/blog/the-self- contained-test The case for WET tests - https://thoughtbot.com/blog/the-case-for-wet- tests 37