tests: Move assertArrayEquals to shared assertions file

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2822>

tests/common/assertions.js

@@ -0,0 +1,17 @@
+/* exported assertArrayEquals */
+
+const JsUnit = imports.jsUnit;
+
+/**
+ * Asserts if two arrays have the same length and each element passes assertEquals
+ *
+ * @template T
+ * @param {string} errorMessage an error message if the arrays are not equal
+ * @param {T[]} array1 the first array
+ * @param {T[]} array2 the second array
+ */
+function assertArrayEquals(errorMessage, array1, array2) {
+    JsUnit.assertEquals(`${errorMessage} length`, array1.length, array2.length);
+    for (let j = 0; j < array1.length; j++)
+        JsUnit.assertEquals(`${errorMessage} item ${j}`, array1[j], array2[j]);
+}