1 files changed, 188 insertions, 0 deletions
diff --git a/spec/lib/gitlab/pagination/keyset/column_order_definition_spec.rb b/spec/lib/gitlab/pagination/keyset/column_order_definition_spec.rb
new file mode 100644
index 00000000000..6e9e987f90c
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+++ b/spec/lib/gitlab/pagination/keyset/column_order_definition_spec.rb
@@ -0,0 +1,188 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Gitlab::Pagination::Keyset::ColumnOrderDefinition do
+  let_it_be(:project_name_column) do
+    described_class.new(
+      attribute_name: :name,
+      order_expression: Project.arel_table[:name].asc,
+      nullable: :not_nullable,
+      distinct: true
+    )
+  end
+
+  let_it_be(:project_name_lower_column) do
+    described_class.new(
+      attribute_name: :name,
+      order_expression: Project.arel_table[:name].lower.desc,
+      nullable: :not_nullable,
+      distinct: true
+    )
+  end
+
+  let_it_be(:project_calculated_column_expression) do
+    # COALESCE("projects"."description", 'No Description')
+    Arel::Nodes::NamedFunction.new('COALESCE', [
+      Project.arel_table[:description],
+      Arel.sql("'No Description'")
+    ])
+  end
+
+  let_it_be(:project_calculated_column) do
+    described_class.new(
+      attribute_name: :name,
+      column_expression: project_calculated_column_expression,
+      order_expression: project_calculated_column_expression.asc,
+      nullable: :not_nullable,
+      distinct: true
+    )
+  end
+
+  describe '#order_direction' do
+    context 'inferring order_direction from order_expression' do
+      it { expect(project_name_column).to be_ascending_order }
+      it { expect(project_name_column).not_to be_descending_order }
+
+      it { expect(project_name_lower_column).to be_descending_order }
+      it { expect(project_name_lower_column).not_to be_ascending_order }
+
+      it { expect(project_calculated_column).to be_ascending_order }
+      it { expect(project_calculated_column).not_to be_descending_order }
+
+      it 'raises error when order direction cannot be infered' do
+        expect do
+          described_class.new(
+            attribute_name: :name,
+            column_expression: Project.arel_table[:name],
+            order_expression: 'name asc',
+            reversed_order_expression: 'name desc',
+            nullable: :not_nullable,
+            distinct: true
+          )
+        end.to raise_error(RuntimeError, /Invalid or missing `order_direction`/)
+      end
+
+      it 'does not raise error when order direction is explicitly given' do
+        column_order_definition = described_class.new(
+          attribute_name: :name,
+          column_expression: Project.arel_table[:name],
+          order_expression: 'name asc',
+          reversed_order_expression: 'name desc',
+          order_direction: :asc,
+          nullable: :not_nullable,
+          distinct: true
+        )
+
+        expect(column_order_definition).to be_ascending_order
+      end
+    end
+  end
+
+  describe '#column_expression' do
+    context 'inferring column_expression from order_expression' do
+      it 'infers the correct column expression' do
+        column_order_definition = described_class.new(attribute_name: :name, order_expression: Project.arel_table[:name].asc)
+
+        expect(column_order_definition.column_expression).to eq(Project.arel_table[:name])
+      end
+
+      it 'raises error when raw string is given as order expression' do
+        expect do
+          described_class.new(attribute_name: :name, order_expression: 'name DESC')
+        end.to raise_error(RuntimeError, /Couldn't calculate the column expression. Please pass an ARel node/)
+      end
+    end
+  end
+
+  describe '#reversed_order_expression' do
+    it 'raises error when order cannot be reversed automatically' do
+      expect do
+        described_class.new(
+          attribute_name: :name,
+          column_expression: Project.arel_table[:name],
+          order_expression: 'name asc',
+          order_direction: :asc,
+          nullable: :not_nullable,
+          distinct: true
+        )
+      end.to raise_error(RuntimeError, /Couldn't determine reversed order/)
+    end
+  end
+
+  describe '#reverse' do
+    it { expect(project_name_column.reverse.order_expression).to eq(Project.arel_table[:name].desc) }
+    it { expect(project_name_column.reverse).to be_descending_order }
+
+    it { expect(project_calculated_column.reverse.order_expression).to eq(project_calculated_column_expression.desc) }
+    it { expect(project_calculated_column.reverse).to be_descending_order }
+
+    context 'when reversed_order_expression is given' do
+      it 'uses the given expression' do
+        column_order_definition = described_class.new(
+          attribute_name: :name,
+          column_expression: Project.arel_table[:name],
+          order_expression: 'name asc',
+          reversed_order_expression: 'name desc',
+          order_direction: :asc,
+          nullable: :not_nullable,
+          distinct: true
+        )
+
+        expect(column_order_definition.reverse.order_expression).to eq('name desc')
+      end
+    end
+  end
+
+  describe '#nullable' do
+    context 'when the column is nullable' do
+      let(:nulls_last_order) do
+        described_class.new(
+          attribute_name: :name,
+          column_expression: Project.arel_table[:name],
+          order_expression: Gitlab::Database.nulls_last_order('merge_request_metrics.merged_at', :desc),
+          reversed_order_expression: Gitlab::Database.nulls_first_order('merge_request_metrics.merged_at', :asc),
+          order_direction: :desc,
+          nullable: :nulls_last, # null values are always last
+          distinct: false
+        )
+      end
+
+      it 'requires the position of the null values in the result' do
+        expect(nulls_last_order).to be_nulls_last
+      end
+
+      it 'reverses nullable correctly' do
+        expect(nulls_last_order.reverse).to be_nulls_first
+      end
+
+      it 'raises error when invalid nullable value is given' do
+        expect do
+          described_class.new(
+            attribute_name: :name,
+            column_expression: Project.arel_table[:name],
+            order_expression: Gitlab::Database.nulls_last_order('merge_request_metrics.merged_at', :desc),
+            reversed_order_expression: Gitlab::Database.nulls_first_order('merge_request_metrics.merged_at', :asc),
+            order_direction: :desc,
+            nullable: true,
+            distinct: false
+          )
+        end.to raise_error(RuntimeError, /Invalid `nullable` is given/)
+      end
+
+      it 'raises error when the column is nullable and distinct' do
+        expect do
+          described_class.new(
+            attribute_name: :name,
+            column_expression: Project.arel_table[:name],
+            order_expression: Gitlab::Database.nulls_last_order('merge_request_metrics.merged_at', :desc),
+            reversed_order_expression: Gitlab::Database.nulls_first_order('merge_request_metrics.merged_at', :asc),
+            order_direction: :desc,
+            nullable: :nulls_last,
+            distinct: true
+          )
+        end.to raise_error(RuntimeError, /Invalid column definition/)
+      end
+    end
+  end
+end