diff --git a/tests/.eslintrc.json b/tests/.eslintrc.json
index d8e4a4e58..9ad47d2d9 100644
--- a/tests/.eslintrc.json
+++ b/tests/.eslintrc.json
@@ -15,7 +15,6 @@
 
 		"new-cap": "warn",
 		"no-undef": "warn",
-		"no-useless-escape": "warn",
-		"strict": "warn"
+		"no-useless-escape": "warn"
 	}
 }
diff --git a/tests/jest.setup.js b/tests/jest.setup.js
index a63a116eb..3cb094332 100644
--- a/tests/jest.setup.js
+++ b/tests/jest.setup.js
@@ -1,3 +1,5 @@
+'use strict';
+
 // Tweak some mw.configs as needed by tests
 mw.config.set({
 	wgPageName: 'Macbeth,_King_of_Scotland',
diff --git a/tests/morebits.array.js b/tests/morebits.array.js
index c64b9d8a9..b8c29542c 100644
--- a/tests/morebits.array.js
+++ b/tests/morebits.array.js
@@ -1,3 +1,5 @@
+'use strict';
+
 describe('Morebits.array', () => {
 	test('chunk', () => {
 		assert.deepEqual(Morebits.array.chunk([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], 3), [[1, 2, 3], [4, 5, 6], [7, 8, 9], [10]], '10 over 3');
diff --git a/tests/morebits.batchOperation.js b/tests/morebits.batchOperation.js
index 76bab9616..06aed974a 100644
--- a/tests/morebits.batchOperation.js
+++ b/tests/morebits.batchOperation.js
@@ -1,3 +1,5 @@
+'use strict';
+
 describe('Morebits.batchOperation', () => {
 	test('Contruction', () => {
 		assert.true(new Morebits.batchOperation() instanceof Morebits.batchOperation, 'Correct instance');
diff --git a/tests/morebits.createHtml.js b/tests/morebits.createHtml.js
index 63563c9e4..07be8fe88 100644
--- a/tests/morebits.createHtml.js
+++ b/tests/morebits.createHtml.js
@@ -1,3 +1,5 @@
+'use strict';
+
 describe('Morebits.createHtml', () => {
 
 	test('createHtml', () => {
diff --git a/tests/morebits.date.js b/tests/morebits.date.js
index 9327c471a..b9d535948 100644
--- a/tests/morebits.date.js
+++ b/tests/morebits.date.js
@@ -1,3 +1,5 @@
+'use strict';
+
 describe('Morebits.date', () => {
 	const now = Date.now();
 	const timestampMediaWiki = '16:26, 7 November 2020 (UTC)', timestampIso = '2020-11-07T16:26:00.000Z', naive = 20201107162600;
diff --git a/tests/morebits.ip.js b/tests/morebits.ip.js
index 06e5b5516..d4f2da800 100644
--- a/tests/morebits.ip.js
+++ b/tests/morebits.ip.js
@@ -1,3 +1,5 @@
+'use strict';
+
 describe('Morebits.ip', () => {
 	test('sanitizeIPv6', () => {
 		assert.strictEqual(Morebits.ip.sanitizeIPv6('2001:0db8:0010:0000:0000:0000:0000:0001'), '2001:DB8:10:0:0:0:0:1', 'Shorten IPv6');
diff --git a/tests/morebits.js b/tests/morebits.js
index 741eb212a..13083740c 100644
--- a/tests/morebits.js
+++ b/tests/morebits.js
@@ -1,3 +1,5 @@
+'use strict';
+
 describe('constants', () => {
 	test('userIsSysop', () => {
 		assert.true(Morebits.userIsSysop, 'Is sysop');
diff --git a/tests/morebits.quickForm.js b/tests/morebits.quickForm.js
index 964aa59dd..de48acb10 100644
--- a/tests/morebits.quickForm.js
+++ b/tests/morebits.quickForm.js
@@ -1,3 +1,5 @@
+'use strict';
+
 /**
  * Simple helper to render a quickform element
  *
diff --git a/tests/morebits.string.js b/tests/morebits.string.js
index cdedfc1f0..bce71c9b9 100644
--- a/tests/morebits.string.js
+++ b/tests/morebits.string.js
@@ -1,3 +1,5 @@
+'use strict';
+
 describe('Morebits.string', () => {
 	test('escapeRegExp', () => {
 		assert.strictEqual(Morebits.string.escapeRegExp('Four score and seven years ago'), 'Four[_ ]score[_ ]and[_ ]seven[_ ]years[_ ]ago', 'Spaces');
diff --git a/tests/morebits.taskManager.js b/tests/morebits.taskManager.js
index b44ad04fc..7d5ea5f00 100644
--- a/tests/morebits.taskManager.js
+++ b/tests/morebits.taskManager.js
@@ -1,3 +1,5 @@
+'use strict';
+
 describe('Morebits.taskManager', () => {
 	test('Contruction', () => {
 		const tm = new Morebits.taskManager();
diff --git a/tests/morebits.unbinder.js b/tests/morebits.unbinder.js
index 2540f457c..98e7362ec 100644
--- a/tests/morebits.unbinder.js
+++ b/tests/morebits.unbinder.js
@@ -1,3 +1,5 @@
+'use strict';
+
 describe('Morebits.unbinder', () => {
 	test('Construction', () => {
 		assert.throws(() => new Morebits.unbinder(), 'throws: no string');
diff --git a/tests/morebits.wikitext.js b/tests/morebits.wikitext.js
index 2bf15abd0..6d7a8b5e1 100644
--- a/tests/morebits.wikitext.js
+++ b/tests/morebits.wikitext.js
@@ -1,3 +1,5 @@
+'use strict';
+
 describe('Morebits.wikitext', () => {
 	test('parseTemplate', () => {
 		// Function to help build a template from a sample object
diff --git a/tests/twinkleblock.test.js b/tests/twinkleblock.test.js
index 732af83da..83ffe60bb 100644
--- a/tests/twinkleblock.test.js
+++ b/tests/twinkleblock.test.js
@@ -1,3 +1,5 @@
+'use strict';
+
 describe('modules/twinkleblock', () => {
 	describe('combineFormDataAndFieldTemplateOptions', () => {
 		// https://github.com/wikimedia-gadgets/twinkle/issues/2106
diff --git a/tests/twinkletag.test.js b/tests/twinkletag.test.js
index dc9586b0d..eeb228d24 100644
--- a/tests/twinkletag.test.js
+++ b/tests/twinkletag.test.js
@@ -1,3 +1,5 @@
+'use strict';
+
 describe('modules/twinkletag', () => {
 	describe('checkIncompatible', () => {
 		test('no conflicts, 0 tags to check', () => {
diff --git a/tests/twinklewarn.test.js b/tests/twinklewarn.test.js
index 3684775a1..5e054df2c 100644
--- a/tests/twinklewarn.test.js
+++ b/tests/twinklewarn.test.js
@@ -1,3 +1,5 @@
+'use strict';
+
 describe('modules/twinklewarn', () => {
 	describe('getTemplateProperty', () => {
 		const templates = {
diff --git a/tests/twinklexfd.test.js b/tests/twinklexfd.test.js
index 0fd9812bb..c895b249d 100644
--- a/tests/twinklexfd.test.js
+++ b/tests/twinklexfd.test.js
@@ -1,3 +1,5 @@
+'use strict';
+
 describe('modules/twinklexfd', () => {
 	describe('insertRMTR', () => {
 		test('0 rows, 1 line breaks', () => {