Added tests and change the relation logic

app/services/calculators/calculation_service.rb

@@ -9,8 +9,12 @@ def initialize(calculator, inputs)
   def perform
     @calculator.formulas.map do |formula|
       result = @dentaku.evaluate(formula.expression, @inputs).round(2)
-
-      { label: formula.label, result: result, unit: formula.unit, relation: formula.relation.downcase }
+      {
+        label: formula.label,
+        result: result,
+        unit: formula.unit,
+        relation: formula.relation
+      }
     end
   end
 end

app/validators/relation_validator.rb

@@ -8,17 +8,17 @@ def validate(record)
   def relation_is_correct(record)
     return if record.formulas.blank?
 
-    if record.formulas.first.relation == "Previous"
+    if record.formulas.first.relation == "previous"
       record.formulas.first.errors.add(:relation, "The first formula cannot have a relation of 'Previous' because there is no previous formula.")
     end
 
-    if record.formulas.last.relation == "Next"
+    if record.formulas.last.relation == "next"
       record.formulas.last.errors.add(:relation, "The last formula cannot have a relation of 'Next' because there is no next formula.")
     end
 
     last_relation = nil
     record.formulas.each do |formula|
-      if last_relation == "Next" && formula.relation == "Previous"
+      if last_relation == "next" && formula.relation == "previous"
         formula.errors.add(:relation, "cannot have the same relation as the previous formula.")
       end
       last_relation = formula.relation

app/views/account/calculators/partials/_formula_fields.html.erb

@@ -9,9 +9,8 @@
 
     <%= f.input :uk_unit, label: "Uk Unit Label:" %>
     <%= f.input :en_unit, label: "Unit Label:" %>
-    <%= f.input :relation, as: :select, label: "Relation of formula (optinal):",
-                collection: ["Next", "Previous"], include_blank: "None"
-    %>
+    <%= f.input :relation, as: :select, label: "Relation of formula (optional):",
+        collection: { "None": nil, "Next": "next", "Previous": "previous"}, default: "None" %>
 
     <%= link_to_remove_association "- Remove Formula", f, class: "text-red-500 underline" %>
   </div>

spec/helpers/calculators/calculation_service_helper_spec.rb

@@ -6,7 +6,7 @@
   let(:calculator) { instance_double("Calculator", formulas: formulas) }
   let(:formulas) do
     [
-      Formula.new(en_label: "Addition", en_unit: "units", uk_label: "Додавання", uk_unit: "одиниці", expression: "x + y"),
+      Formula.new(en_label: "Addition", en_unit: "units", uk_label: "Додавання", uk_unit: "одиниці", expression: "x + y", relation: "next"),
       Formula.new(en_label: "Multiplication", en_unit: "units", uk_label: "Множення", uk_unit: "одиниці", expression: "x * y")
     ]
   end
@@ -28,8 +28,8 @@
 
       it "returns results with English labels and units" do
         expect(subject).to eq([
-          { label: "Addition", result: 8, unit: "units" },
-          { label: "Multiplication", result: 15, unit: "units" }
+          { label: "Addition", result: 8, unit: "units", relation: "next" },
+          { label: "Multiplication", result: 15, unit: "units", relation: nil }
         ])
       end
     end
@@ -39,8 +39,8 @@
 
       it "returns results with Ukrainian labels and units" do
         expect(subject).to eq([
-          { label: "Додавання", result: 8, unit: "одиниці" },
-          { label: "Множення", result: 15, unit: "одиниці" }
+          { label: "Додавання", result: 8, unit: "одиниці", relation: "next" },
+          { label: "Множення", result: 15, unit: "одиниці", relation: nil }
         ])
       end
     end

spec/validators/relation_validator_spec.rb

@@ -0,0 +1,56 @@
+require "rails_helper"
+
+RSpec.describe RelationValidator do
+  let(:calculator) { build(:calculator) }
+
+  describe "validations" do
+    let(:formula_1) { build(:formula, relation: "previous") }
+    let(:formula_2) { build(:formula, relation: "next") }
+    let(:formula_3) { build(:formula, relation: nil) }
+
+    context "when the first formula has a relation of 'Previous'" do
+      before do
+        calculator.formulas = [formula_1]
+        calculator.valid?
+      end
+
+      it "adds an error to the first formula" do
+        expect(formula_1.errors[:relation]).to include("The first formula cannot have a relation of 'Previous' because there is no previous formula.")
+      end
+    end
+
+    context "when the last formula has a relation of 'Next'" do
+      before do
+        calculator.formulas = [formula_2]
+        calculator.valid?
+      end
+
+      it "adds an error to the last formula" do
+        expect(formula_2.errors[:relation]).to include("The last formula cannot have a relation of 'Next' because there is no next formula.")
+      end
+    end
+
+    context "when formulas have consecutive relations 'Next' and 'Previous'" do
+      before do
+        calculator.formulas = [formula_2, formula_1]
+        calculator.valid?
+      end
+
+      it "adds an error to the second formula" do
+        expect(formula_1.errors[:relation]).to include("cannot have the same relation as the previous formula.")
+      end
+    end
+
+    context "when all formulas have valid relations" do
+      before do
+        calculator.formulas = [formula_3, formula_1]
+        calculator.valid?
+      end
+
+      it "does not add errors to the formulas" do
+        expect(formula_1.errors[:relation]).to be_empty
+        expect(formula_3.errors[:relation]).to be_empty
+      end
+    end
+  end
+end