pagination: add paginator tests.

test/unit/paginator_test.rb

@@ -0,0 +1,34 @@
+require 'test_helper'
+
+class PaginatorTest < ActiveSupport::TestCase
+  setup do
+    @posts = FactoryBot.create_list(:post, 5)
+  end
+
+  context "sequential pagination (before)" do
+    should "return the correct set of records" do
+      expected_posts = Post.limit(3).order(id: :desc)
+      posts = Post.paginate("b9999999", limit: 3)
+
+      assert_equal(expected_posts.map(&:id), posts.map(&:id))
+    end
+  end
+
+  context "sequential pagination (after)" do
+    should "return the correct set of records" do
+      expected_posts = Post.limit(3).order(id: :asc).reverse
+      posts = Post.paginate("a0", limit: 3)
+
+      assert_equal(expected_posts.map(&:id), posts.map(&:id))
+    end
+  end
+
+  context "numbered pagination" do
+    should "return the correct set of records" do
+      expected_posts = Post.limit(3).order(id: :desc)
+      posts = Post.order(id: :desc).paginate("1", limit: 3)
+
+      assert_equal(expected_posts.map(&:id), posts.map(&:id))
+    end
+  end
+end