Add tests for populate option in paginate

tests/unit/models/plugins/paginate.plugin.test.js

@@ -0,0 +1,61 @@
+const mongoose = require('mongoose');
+const setupTestDB = require('../../../utils/setupTestDB');
+const paginate = require('../../../../src/models/plugins/paginate.plugin');
+
+const projectSchema = mongoose.Schema({
+  name: {
+    type: String,
+    required: true,
+  },
+});
+
+projectSchema.virtual('tasks', {
+  ref: 'Task',
+  localField: '_id',
+  foreignField: 'project',
+});
+
+projectSchema.plugin(paginate);
+const Project = mongoose.model('Project', projectSchema);
+
+const taskSchema = mongoose.Schema({
+  name: {
+    type: String,
+    required: true,
+  },
+  project: {
+    type: mongoose.SchemaTypes.ObjectId,
+    ref: 'Project',
+    required: true,
+  },
+});
+
+taskSchema.plugin(paginate);
+const Task = mongoose.model('Task', taskSchema);
+
+setupTestDB();
+
+describe('paginate plugin', () => {
+  describe('populate option', () => {
+    test('should populate the specified data fields', async () => {
+      const project = await Project.create({ name: 'Project One' });
+      const task = await Task.create({ name: 'Task One', project: project._id });
+
+      const taskPages = await Task.paginate({ _id: task._id }, { populate: 'project' });
+
+      expect(taskPages.results[0].project).toHaveProperty('_id', project._id);
+    });
+
+    test('should populate nested fields', async () => {
+      const project = await Project.create({ name: 'Project One' });
+      const task = await Task.create({ name: 'Task One', project: project._id });
+
+      const projectPages = await Project.paginate({ _id: project._id }, { populate: 'tasks.project' });
+      const { tasks } = projectPages.results[0];
+
+      expect(tasks).toHaveLength(1);
+      expect(tasks[0]).toHaveProperty('_id', task._id);
+      expect(tasks[0].project).toHaveProperty('_id', project._id);
+    });
+  });
+});