Add a couple of basic unit-tests for PDFPageViewBuffer

The `PDFPageViewBuffer`-code is very important for the correct function of the viewer, but it's currently not tested at all.
While the `PDFPageViewBuffer` is obviously intended to be used with `PDFPageView`-instances, it only accesses a couple of `PDFPageView` properties/methods and consequently it's fairly easy to unit-test this code with dummy-data.

These unit-tests should help improve our confidence in this code, and will also come in handy with other changes that I'm working on (regarding modernizing and re-factoring the `PDFPageViewBuffer`-code).

test/unit/base_viewer_spec.js

@@ -0,0 +1,162 @@
+/* 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/base_viewer.js";
+
+describe("BaseViewer", 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._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._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._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._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._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._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._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, 3]));
+
+      expect(buffer._buffer).toEqual([
+        viewsMap.get(1),
+        viewsMap.get(2),
+        viewsMap.get(3),
+      ]);
+    });
+
+    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);
+    });
+  });
+});

test/unit/clitests.json

@@ -9,6 +9,7 @@
     "annotation_spec.js",
     "annotation_storage_spec.js",
     "api_spec.js",
+    "base_viewer_spec.js",
     "bidi_spec.js",
     "cff_parser_spec.js",
     "cmap_spec.js",

test/unit/jasmine-boot.js

@@ -54,6 +54,7 @@ async function initializePDFJS(callback) {
       "pdfjs-test/unit/annotation_spec.js",
       "pdfjs-test/unit/annotation_storage_spec.js",
       "pdfjs-test/unit/api_spec.js",
+      "pdfjs-test/unit/base_viewer_spec.js",
       "pdfjs-test/unit/bidi_spec.js",
       "pdfjs-test/unit/cff_parser_spec.js",
       "pdfjs-test/unit/cmap_spec.js",

web/base_viewer.js

@@ -127,6 +127,17 @@ function PDFPageViewBuffer(size) {
   this.has = function (view) {
     return data.includes(view);
   };
+
+  if (
+    typeof PDFJSDev === "undefined" ||
+    PDFJSDev.test("!PRODUCTION || TESTING")
+  ) {
+    Object.defineProperty(this, "_buffer", {
+      get() {
+        return data.slice();
+      },
+    });
+  }
 }
 
 function isSameScale(oldScale, newScale) {
@@ -1879,4 +1890,4 @@ class BaseViewer {
   }
 }
 
-export { BaseViewer };
+export { BaseViewer, PDFPageViewBuffer };