Add a FakeSignatureVerifier for development mode and TESTING builds (PR 21247 follow-up)

Despite the `enableSignatureVerification` option/preference being enabled in development mode and TESTING builds, the lack of any `SignatureVerifier` implementation still renders the UI disabled.
This seems unfortunate, since it makes it more difficult to check that the digital signature UI works correctly:
 - That the button is visible when it's supposed to be, and that the panel can be opened/closed.
 - That the UI looks correct, w.r.t. the HTML elements and their CSS rules.
 - Currently the viewer JS code is effectively uncovered, with overall test-coverage dropping from `90` to `89` percent when PR 21247 landed.

To improve the current situation this patch adds a `FakeSignatureVerifier` class, limited to only development mode and TESTING builds, that treats every digital signature as invalid.
This allows easier manual testing, and also the addition of a few *very rudimentary* integration-tests.

*Note:* It probably wouldn't be all that difficult to add additional integration-tests for *valid* certificates, by having the test-cases instruct (during setup) the `FakeSignatureVerifier` how to respond to simulate verified certificates.

test/integration/digital_signature_spec.mjs

@@ -0,0 +1,107 @@
+/* Copyright 2026 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 { closePages, FSI, loadAndWait, PDI } from "./test_utils.mjs";
+
+describe("Digital signatures", () => {
+  describe("Document without signatures", () => {
+    let pages;
+
+    beforeEach(async () => {
+      pages = await loadAndWait("tracemonkey.pdf", ".textLayer .endOfContent");
+    });
+
+    afterEach(async () => {
+      await closePages(pages);
+    });
+
+    it("check that the signatureProperties button is hidden", async () => {
+      await Promise.all(
+        pages.map(async ([browserName, page]) => {
+          const buttonHidden = await page.$eval(
+            "#signatureProperties",
+            el => el.hidden
+          );
+          expect(buttonHidden).withContext(`In ${browserName}`).toBeTrue();
+
+          const separatorHidden = await page.$eval(
+            "#signaturePropertiesSeparator",
+            el => el.hidden
+          );
+          expect(separatorHidden).withContext(`In ${browserName}`).toBeTrue();
+        })
+      );
+    });
+  });
+
+  describe("Document with signatures", () => {
+    let pages;
+
+    beforeEach(async () => {
+      pages = await loadAndWait("issue20433.pdf", ".textLayer .endOfContent");
+    });
+
+    afterEach(async () => {
+      await closePages(pages);
+    });
+
+    it("check that the signatureProperties button is visible", async () => {
+      await Promise.all(
+        pages.map(async ([browserName, page]) => {
+          const buttonHidden = await page.$eval(
+            "#signatureProperties",
+            el => el.hidden
+          );
+          expect(buttonHidden).withContext(`In ${browserName}`).toBeFalse();
+
+          const separatorHidden = await page.$eval(
+            "#signaturePropertiesSeparator",
+            el => el.hidden
+          );
+          expect(separatorHidden).withContext(`In ${browserName}`).toBeFalse();
+        })
+      );
+    });
+
+    it("check that the signatureProperties panel contains two signatures", async () => {
+      await Promise.all(
+        pages.map(async ([browserName, page]) => {
+          await page.click("#signatureProperties");
+          await page.waitForSelector("#signaturePropertiesPanel", {
+            hidden: false,
+          });
+
+          await page.waitForFunction(
+            `document.getElementById("signaturePropertiesBanner").textContent !== ""`
+          );
+          const bannerMsg = await page.$eval(
+            "#signaturePropertiesBanner",
+            el => el.textContent
+          );
+          expect(bannerMsg)
+            .withContext(`In ${browserName}`)
+            .toEqual(
+              `Document signed but ${FSI}2${PDI} digital signatures could not be verified`
+            );
+
+          await page.keyboard.press("Escape");
+          await page.waitForSelector("#signaturePropertiesPanel", {
+            hidden: true,
+          });
+        })
+      );
+    });
+  });
+});

test/integration/jasmine-boot.js

@@ -34,6 +34,7 @@ async function runTests(results) {
       "comment_spec.mjs",
       "copy_paste_spec.mjs",
       "cursor_tools_spec.mjs",
+      "digital_signature_spec.mjs",
       "document_properties_spec.mjs",
       "find_spec.mjs",
       "freetext_editor_spec.mjs",

web/external_services.js

@@ -61,8 +61,7 @@ class BaseExternalServices {
    * Properties UI should subclass `BaseExternalServices` and return
    * an object exposing `verify(signature)` (and optionally
    * `viewCertificate(certificate)`) that resolves to a
-   * `VerificationResult` — see `web/firefoxcom.js` for the exact
-   * shape.
+   * `VerificationResult` — see `web/firefoxcom.js` for the exact shape.
    *
    * @returns {Object|null}
    */

web/genericcom.js

@@ -66,6 +66,13 @@ class ExternalServices extends BaseExternalServices {
   createSignatureStorage(eventBus, signal) {
     return new SignatureStorage(eventBus, signal);
   }
+
+  createSignatureVerifier() {
+    if (typeof PDFJSDev === "undefined" || PDFJSDev.test("TESTING")) {
+      return new FakeSignatureVerifier();
+    }
+    return null;
+  }
 }
 
 class MLManager {
@@ -166,6 +173,33 @@ if (typeof PDFJSDev === "undefined" || PDFJSDev.test("TESTING")) {
       this.enableGuessAltText = enabled;
     }
   };
+
+  // eslint-disable-next-line no-var
+  var FakeSignatureVerifier = class {
+    async verify(signature) {
+      if (signature.signatureType === null) {
+        return {
+          status: "unknown",
+          errorCode: "SUBFILTER_NOT_SUPPORTED",
+          message: signature.subFilter,
+          certificate: null,
+          documentModifiedAfterSigning: !signature.coversWholeDocument,
+        };
+      }
+
+      return {
+        status: "unknown",
+        errorCode: "EMPTY_RESPONSE",
+        message: null,
+        certificate: null,
+        documentModifiedAfterSigning: !signature.coversWholeDocument,
+      };
+    }
+
+    async viewCertificate(certificate) {
+      return false;
+    }
+  };
 }
 
 export { ExternalServices, initCom, MLManager, Preferences };