1 files changed, 34 insertions, 0 deletions
diff --git a/toolkit/components/resistfingerprinting/tests/browser/head.js b/toolkit/components/resistfingerprinting/tests/browser/head.js
index e2fddaecc6..2a1b52f1c0 100644
--- a/toolkit/components/resistfingerprinting/tests/browser/head.js
+++ b/toolkit/components/resistfingerprinting/tests/browser/head.js
@@ -52,6 +52,40 @@ function countDifferencesInArrayBuffers(buffer1, buffer2) {
   return differences;
 }
 
+function isDataRandomizedFuzzy(name, data1, data2, isCompareOriginal) {
+  let diffCnt = countDifferencesInUint8Arrays(data1, data2);
+  info(`For ${name} there are ${diffCnt} bits are different.`);
+
+  // The Canvas randomization adds at most 512 bits noise to the image data.
+  // We compare the image data arrays to see if they are different and the
+  // difference is within the range.
+
+  // If we are compare two randomized arrays, the difference can be doubled.
+  let expected = isCompareOriginal
+    ? NUM_RANDOMIZED_CANVAS_BITS
+    : NUM_RANDOMIZED_CANVAS_BITS * 2;
+
+  // The number of difference bits should never bigger than the expected
+  // number. It could be zero if the randomization is disabled.
+  Assert.lessOrEqual(
+    diffCnt,
+    expected,
+    "The number of noise bits is expected."
+  );
+
+  return diffCnt <= expected && diffCnt > 0;
+}
+
+function isDataRandomizedNotEqual(name, data1, data2) {
+  return data1 !== data2;
+}
+
+function isDataRandomizedGreaterThanZero(name, data1, data2) {
+  let diffCnt = countDifferencesInArrayBuffers(data1, data2);
+  info(`For ${name} there are ${diffCnt} bits are different.`);
+  return diffCnt > 0;
+}
+
 function promiseObserver(topic) {
   return new Promise(resolve => {
     let obs = (aSubject, aTopic) => {