diff --git a/tests/bootstrap.js b/tests/bootstrap.js
index fe345d2cc..0310b32bf 100644
--- a/tests/bootstrap.js
+++ b/tests/bootstrap.js
@@ -58,6 +58,11 @@
     // from somewhere in tests/.
     root: window.location.href.replace(/\/tests\/.*$/, '/'),
 
+    // List of deps files to load.  Paths relative to root.
+    depsFiles: [
+      'build/deps.js',
+    ],
+    
     // List of goog.modules to goog.require.
     requires: [
       'Blockly',
@@ -69,7 +74,8 @@
       'Blockly.Python.all',
     ],
 
-    // List of scripts to load in compressed mode, instead of requires.
+    // List of scripts to load in compressed mode, instead of
+    // requires.  Paths relative to root.
     compressedScripts: [
       'blockly_compressed.js',
       'blocks_compressed.js',
@@ -82,6 +88,7 @@
 
     // Additional scripts to be loaded after Blockly is loaded,
     // whether Blockly is loaded from compressed or uncompressed.
+    // Paths relative to root.
     additionalScripts: [
       'msg/messages.js',
     ],
@@ -112,10 +119,15 @@
     // goog.module).
     document.write(
         '<script src="' + options.root + '/closure/goog/base.js"></script>');
-    // Load dependency graph info from build/deps.js.  To update
-    // deps.js, run `npm run build:deps`.
-    document.write(
-        '<script src="' + options.root + '/build/deps.js"></script>');
+
+    // Load dependency graph info from the specified deps files -
+    // typically just build/deps.js.  To update deps after changing
+    // any module's goog.requires / imports, run `npm run build:deps`.
+    for (let i = 0; i < options.depsFiles.length; i++) {
+      document.write(
+          '<script src="' + options.root + options.depsFiles[i] + '">' +
+              '</script>');
+    }
 
     const requiresString = options.requires.map(quote).join();
     const scriptsString = options.additionalScripts.map(quote).join();
diff --git a/tests/mocha/.mocharc.js b/tests/mocha/.mocharc.js
index 3c156db3e..0928b25d2 100644
--- a/tests/mocha/.mocharc.js
+++ b/tests/mocha/.mocharc.js
@@ -2,6 +2,5 @@
 
 module.exports = {
   ui: 'tdd',
-  file: '../blockly_uncompressed.js',
   reporter: 'landing'
 };
diff --git a/tests/mocha/index.html b/tests/mocha/index.html
index c3caf1469..e63dc1f6a 100644
--- a/tests/mocha/index.html
+++ b/tests/mocha/index.html
@@ -5,9 +5,6 @@
     <title>Mocha Tests for Blockly</title>
 
     <link href="../../node_modules/mocha/mocha.css" rel="stylesheet" />
-    <script src="../../blockly_uncompressed.js"></script>
-    <script src="../../build/deps.mocha.js"></script>
-    <script src="../../msg/messages.js"></script>
   </head>
   <style>
     #blocklyDiv {
@@ -21,6 +18,9 @@
     <div id="mocha"></div>
     <div id="failureCount" style="display:none" tests_failed="unset"></div>
     <div id="failureMessages" style="display:none"></div>
+    <!-- Load mocha et al. before bootstrapping so that we can safely
+	 goog.require() the test modules that make calls to (e.g.)
+	 suite() at the top level. -->
     <script src="../../node_modules/chai/chai.js"></script>
     <script src="../../node_modules/mocha/mocha.js"></script>
     <script src="../../node_modules/sinon/pkg/sinon.js"></script>
@@ -29,92 +29,95 @@
         ui: 'tdd',
         failZero: true,
       });
-    </script>
 
-    <script>
-      // Require optional modules needed by tests.
-      goog.require('Blockly.Dart');
-      goog.require('Blockly.Dart.texts');
-      goog.require('Blockly.JavaScript');
-      goog.require('Blockly.JavaScript.texts');
-      goog.require('Blockly.Lua');
-      goog.require('Blockly.Lua.texts');
-      goog.require('Blockly.PHP');
-      goog.require('Blockly.PHP.texts');
-      goog.require('Blockly.Python');
-      goog.require('Blockly.Python.texts');
-      goog.require('Blockly.libraryBlocks.colour');
-      goog.require('Blockly.libraryBlocks.logic');
-      goog.require('Blockly.libraryBlocks.lists');
-      goog.require('Blockly.libraryBlocks.loops');
-      goog.require('Blockly.libraryBlocks.math');
-      goog.require('Blockly.libraryBlocks.procedures');
-      goog.require('Blockly.libraryBlocks.texts');
-      goog.require('Blockly.libraryBlocks.variables');
-      goog.require('Blockly.libraryBlocks.variablesDynamic');
+      var BLOCKLY_BOOTSTRAP_OPTIONS = {
+	loadCompressed: false,
+	depsFiles: ['build/deps.js', 'build/deps.mocha.js'],
+	requires: [
+	  // Blockly modules needed by tests.
+	  'Blockly',
+	  'Blockly.libraryBlocks',
+	  'Blockly.Dart',
+	  'Blockly.Dart.texts',
+	  'Blockly.JavaScript',
+	  'Blockly.JavaScript.texts',
+	  'Blockly.Lua',
+	  'Blockly.Lua.texts',
+	  'Blockly.PHP',
+	  'Blockly.PHP.texts',
+	  'Blockly.Python',
+	  'Blockly.Python.texts',
 
-      // Run tests.
-      goog.require('Blockly.test.astNode');
-      goog.require('Blockly.test.blockChangeEvent');
-      goog.require('Blockly.test.blockCreateEvent');
-      goog.require('Blockly.test.blockJson');
-      goog.require('Blockly.test.blocks');
-      goog.require('Blockly.test.comments');
-      goog.require('Blockly.test.commentDeserialization');
-      goog.require('Blockly.test.connectionChecker');
-      goog.require('Blockly.test.connectionDb');
-      goog.require('Blockly.test.connection');
-      goog.require('Blockly.test.contextMenuItem');
-      goog.require('Blockly.test.cursor');
-      goog.require('Blockly.test.dropdown');
-      goog.require('Blockly.test.event');
-      goog.require('Blockly.test.extensions');
-      goog.require('Blockly.test.fieldAngle');
-      goog.require('Blockly.test.fieldCheckbox');
-      goog.require('Blockly.test.fieldColour');
-      goog.require('Blockly.test.fieldDropdown');
-      goog.require('Blockly.test.fieldImage');
-      goog.require('Blockly.test.fieldLabelSerialization');
-      goog.require('Blockly.test.fieldLabel');
-      goog.require('Blockly.test.fieldMultiline');
-      goog.require('Blockly.test.fieldNumber');
-      goog.require('Blockly.test.fieldRegistry');
-      goog.require('Blockly.test.fieldTest');
-      goog.require('Blockly.test.fieldTextInput');
-      goog.require('Blockly.test.fieldVariable');
-      goog.require('Blockly.test.flyout');
-      goog.require('Blockly.test.generator');
-      goog.require('Blockly.test.gesture');
-      goog.require('Blockly.test.input');
-      goog.require('Blockly.test.insertionMarker');
-      goog.require('Blockly.test.jsoDeserialization');
-      goog.require('Blockly.test.jsoSerialization');
-      goog.require('Blockly.test.json');
-      goog.require('Blockly.test.keydown');
-      goog.require('Blockly.test.lists');
-      goog.require('Blockly.test.logicTernary');
-      goog.require('Blockly.test.metrics');
-      goog.require('Blockly.test.mutator');
-      goog.require('Blockly.test.names');
-      goog.require('Blockly.test.procedures');
-      goog.require('Blockly.test.registry');
-      goog.require('Blockly.test.serialization');
-      goog.require('Blockly.test.shortcutRegistry');
-      goog.require('Blockly.test.theme');
-      goog.require('Blockly.test.toolbox');
-      goog.require('Blockly.test.tooltip');
-      goog.require('Blockly.test.trashcan');
-      goog.require('Blockly.test.utils');
-      goog.require('Blockly.test.variableMap');
-      goog.require('Blockly.test.variableModel');
-      goog.require('Blockly.test.variables');
-      goog.require('Blockly.test.widgetDiv');
-      goog.require('Blockly.test.workspaceComment');
-      goog.require('Blockly.test.workspaceSvg');
-      goog.require('Blockly.test.workspace');
-      goog.require('Blockly.test.xml');
-      goog.require('Blockly.test.zoomControls');
+	  // Test modules.
+	  'Blockly.test.astNode',
+	  'Blockly.test.blockChangeEvent',
+	  'Blockly.test.blockCreateEvent',
+	  'Blockly.test.blockJson',
+	  'Blockly.test.blocks',
+	  'Blockly.test.comments',
+	  'Blockly.test.commentDeserialization',
+	  'Blockly.test.connectionChecker',
+	  'Blockly.test.connectionDb',
+	  'Blockly.test.connection',
+	  'Blockly.test.contextMenuItem',
+	  'Blockly.test.cursor',
+	  'Blockly.test.dropdown',
+	  'Blockly.test.event',
+	  'Blockly.test.extensions',
+	  'Blockly.test.fieldAngle',
+	  'Blockly.test.fieldCheckbox',
+	  'Blockly.test.fieldColour',
+	  'Blockly.test.fieldDropdown',
+	  'Blockly.test.fieldImage',
+	  'Blockly.test.fieldLabelSerialization',
+	  'Blockly.test.fieldLabel',
+	  'Blockly.test.fieldMultiline',
+	  'Blockly.test.fieldNumber',
+	  'Blockly.test.fieldRegistry',
+	  'Blockly.test.fieldTest',
+	  'Blockly.test.fieldTextInput',
+	  'Blockly.test.fieldVariable',
+	  'Blockly.test.flyout',
+	  'Blockly.test.generator',
+	  'Blockly.test.gesture',
+	  'Blockly.test.input',
+	  'Blockly.test.insertionMarker',
+	  'Blockly.test.jsoDeserialization',
+	  'Blockly.test.jsoSerialization',
+	  'Blockly.test.json',
+	  'Blockly.test.keydown',
+	  'Blockly.test.lists',
+	  'Blockly.test.logicTernary',
+	  'Blockly.test.metrics',
+	  'Blockly.test.mutator',
+	  'Blockly.test.names',
+	  'Blockly.test.procedures',
+	  'Blockly.test.registry',
+	  'Blockly.test.serialization',
+	  'Blockly.test.shortcutRegistry',
+	  'Blockly.test.theme',
+	  'Blockly.test.toolbox',
+	  'Blockly.test.tooltip',
+	  'Blockly.test.trashcan',
+	  'Blockly.test.utils',
+	  'Blockly.test.variableMap',
+	  'Blockly.test.variableModel',
+	  'Blockly.test.variables',
+	  'Blockly.test.widgetDiv',
+	  'Blockly.test.workspaceComment',
+	  'Blockly.test.workspaceSvg',
+	  'Blockly.test.workspace',
+	  'Blockly.test.xml',
+	  'Blockly.test.zoomControls',
+	],
+	additionalScripts: [
+	  'msg/messages.js',
+	  'tests/playgrounds/screenshot.js',
+	  'node_modules/@blockly/dev-tools/dist/index.js',
+	],
+      }
     </script>
+    <script src="../bootstrap.js"></script>
 
     <div id="blocklyDiv"></div>
 
@@ -175,7 +178,10 @@
       <block type="test_field_block"></block>
     </xml>
 
-    <script>
+    <script type=module>
+      // Wait for Blockly to finish loading before running tests.
+      import Blockly from "../blockly.mjs";
+
       let runner = mocha.run(function(failures) {
         var failureDiv = document.getElementById('failureCount');
         failureDiv.setAttribute('tests_failed', failures);