DEV: add a remove_step method to Wizard (#24063)

Using Wizard.exclude_steps applies to all sites in a multisite cluster.
In order to exclude steps for individual sites at run-time, a new
instance method `remove_step` is being added.

spec/lib/wizard/wizard_spec.rb

@@ -56,6 +56,68 @@ RSpec.describe Wizard do
     end
   end
 
+  describe "remove_step" do
+    let(:user) { Fabricate.build(:moderator) }
+    let(:wizard) { Wizard.new(user) }
+    let(:step1) { wizard.create_step("first-step") }
+    let(:step2) { wizard.create_step("second-step") }
+    let(:step3) { wizard.create_step("third-step") }
+
+    before do
+      wizard.append_step(step1)
+      wizard.append_step(step2)
+      wizard.append_step(step3)
+    end
+
+    it "does nothing if step id doesn't match any steps" do
+      wizard.remove_step("nope")
+      expect(wizard.steps).to contain_exactly(step1, step2, step3)
+      expect(wizard.start).to eq(step1)
+    end
+
+    it "can remove the first step" do
+      wizard.remove_step(step1.id)
+      expect(wizard.steps).to contain_exactly(step2, step3)
+      expect(step2.index).to eq(0)
+      expect(step2.previous).to be_blank
+      expect(step2.next).to eq(step3)
+
+      expect(step3.index).to eq(1)
+      expect(step3.previous).to eq(step2)
+      expect(step3.next).to be_blank
+
+      expect(wizard.start).to eq(step2)
+    end
+
+    it "can remove a middle step" do
+      wizard.remove_step(step2.id)
+      expect(wizard.steps).to contain_exactly(step1, step3)
+      expect(step1.index).to eq(0)
+      expect(step1.previous).to be_blank
+      expect(step1.next).to eq(step3)
+
+      expect(step3.index).to eq(1)
+      expect(step3.previous).to eq(step1)
+      expect(step3.next).to be_blank
+
+      expect(wizard.start).to eq(step1)
+    end
+
+    it "can remove the last step" do
+      wizard.remove_step(step3.id)
+      expect(wizard.steps).to contain_exactly(step1, step2)
+      expect(step1.index).to eq(0)
+      expect(step1.previous).to be_blank
+      expect(step1.next).to eq(step2)
+
+      expect(step2.index).to eq(1)
+      expect(step2.previous).to eq(step1)
+      expect(step2.next).to be_blank
+
+      expect(wizard.start).to eq(step1)
+    end
+  end
+
   describe ".exclude_step" do
     let(:user) { Fabricate.build(:moderator) }
     let(:wizard) { Wizard.new(user) }