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Testing PDF Page View Buffer Implementation in Mozilla pdf.js

This test suite validates the PDFPageViewBuffer functionality in Mozilla’s pdf.js library, focusing on buffer management and page view handling for PDF document rendering. The tests ensure proper implementation of view buffering, resizing, and state management.

Test Coverage Overview

The test suite provides comprehensive coverage of PDFPageViewBuffer operations:

Push operations for adding views to buffer
Buffer resizing with and without specific IDs to keep
View presence verification using ‘has’ method
Edge cases for buffer capacity management
View eviction behavior testing

Implementation Analysis

The testing approach utilizes Jest-style unit tests with describe/it blocks for structured test organization. The implementation employs helper functions for test data setup and validates buffer operations through explicit state checks. The tests leverage ES6 Map and Set data structures for view management.

Technical Details

Testing infrastructure includes:

Jest testing framework
ES6 Map/Set implementations
Custom view mocking utilities
Modular test organization
Integration with pdf.js web components

Best Practices Demonstrated

The test suite exemplifies several testing best practices:

Isolated test cases with clear assertions
Comprehensive edge case coverage
Helper functions for test data setup
Consistent test structure and organization
Clear test descriptions and expectations

mozilla/pdfJs

test/unit/pdf_viewer_spec.js

            
/* Copyright 2021 Mozilla Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import { PDFPageViewBuffer } from "../../web/pdf_viewer.js";

describe("PDFViewer", function () {
  describe("PDFPageViewBuffer", function () {
    function createViewsMap(startId, endId) {
      const map = new Map();

      for (let id = startId; id <= endId; id++) {
        map.set(id, {
          id,
          destroy: () => {},
        });
      }
      return map;
    }

    it("handles `push` correctly", function () {
      const buffer = new PDFPageViewBuffer(3);

      const viewsMap = createViewsMap(1, 5),
        iterator = viewsMap.values();

      for (let i = 0; i < 3; i++) {
        const view = iterator.next().value;
        buffer.push(view);
      }
      // Ensure that the correct views are inserted.
      expect([...buffer]).toEqual([
        viewsMap.get(1),
        viewsMap.get(2),
        viewsMap.get(3),
      ]);

      for (let i = 3; i < 5; i++) {
        const view = iterator.next().value;
        buffer.push(view);
      }
      // Ensure that the correct views are evicted.
      expect([...buffer]).toEqual([
        viewsMap.get(3),
        viewsMap.get(4),
        viewsMap.get(5),
      ]);
    });

    it("handles `resize` correctly", function () {
      const buffer = new PDFPageViewBuffer(5);

      const viewsMap = createViewsMap(1, 5),
        iterator = viewsMap.values();

      for (let i = 0; i < 5; i++) {
        const view = iterator.next().value;
        buffer.push(view);
      }
      // Ensure that keeping the size constant won't evict any views.
      buffer.resize(5);

      expect([...buffer]).toEqual([
        viewsMap.get(1),
        viewsMap.get(2),
        viewsMap.get(3),
        viewsMap.get(4),
        viewsMap.get(5),
      ]);

      // Ensure that increasing the size won't evict any views.
      buffer.resize(10);

      expect([...buffer]).toEqual([
        viewsMap.get(1),
        viewsMap.get(2),
        viewsMap.get(3),
        viewsMap.get(4),
        viewsMap.get(5),
      ]);

      // Ensure that decreasing the size will evict the correct views.
      buffer.resize(3);

      expect([...buffer]).toEqual([
        viewsMap.get(3),
        viewsMap.get(4),
        viewsMap.get(5),
      ]);
    });

    it("handles `resize` correctly, with `idsToKeep` provided", function () {
      const buffer = new PDFPageViewBuffer(5);

      const viewsMap = createViewsMap(1, 5),
        iterator = viewsMap.values();

      for (let i = 0; i < 5; i++) {
        const view = iterator.next().value;
        buffer.push(view);
      }
      // Ensure that keeping the size constant won't evict any views,
      // while re-ordering them correctly.
      buffer.resize(5, new Set([1, 2]));

      expect([...buffer]).toEqual([
        viewsMap.get(3),
        viewsMap.get(4),
        viewsMap.get(5),
        viewsMap.get(1),
        viewsMap.get(2),
      ]);

      // Ensure that increasing the size won't evict any views,
      // while re-ordering them correctly.
      buffer.resize(10, new Set([3, 4, 5]));

      expect([...buffer]).toEqual([
        viewsMap.get(1),
        viewsMap.get(2),
        viewsMap.get(3),
        viewsMap.get(4),
        viewsMap.get(5),
      ]);

      // Ensure that decreasing the size will evict the correct views,
      // while re-ordering the remaining ones correctly.
      buffer.resize(3, new Set([1, 2, 5]));

      expect([...buffer]).toEqual([
        viewsMap.get(1),
        viewsMap.get(2),
        viewsMap.get(5),
      ]);
    });

    it("handles `has` correctly", function () {
      const buffer = new PDFPageViewBuffer(3);

      const viewsMap = createViewsMap(1, 2),
        iterator = viewsMap.values();

      for (let i = 0; i < 1; i++) {
        const view = iterator.next().value;
        buffer.push(view);
      }
      expect(buffer.has(viewsMap.get(1))).toEqual(true);
      expect(buffer.has(viewsMap.get(2))).toEqual(false);
    });
  });
});