diff --git a/tests/jsunit/index.html b/tests/jsunit/index.html
index 29a3e4d51..cf10ff987 100644
--- a/tests/jsunit/index.html
+++ b/tests/jsunit/index.html
@@ -20,7 +20,6 @@
     <script src="event_test.js"></script>
     <script src="extensions_test.js"></script>
     <script src="generator_test.js"></script>
-    <script src="json_test.js"></script>
     <script src="variables_test.js"></script>
     <script src="variable_map_test.js"></script>
     <script src="variable_model_test.js"></script>
diff --git a/tests/jsunit/json_test.js b/tests/jsunit/json_test.js
deleted file mode 100644
index 197b8b620..000000000
--- a/tests/jsunit/json_test.js
+++ /dev/null
@@ -1,356 +0,0 @@
-/**
- * @license
- * Copyright 2017 Google LLC
- * SPDX-License-Identifier: Apache-2.0
- */
-'use strict';
-
-/**  Ensure a block can be instantiated from a JSON definition.  */
-function test_json_minimal() {
-  var BLOCK_TYPE = 'test_json_minimal';
-
-  var workspace = new Blockly.Workspace();
-  var block;
-  try {
-    var warnings = captureWarnings(function() {
-      Blockly.defineBlocksWithJsonArray([{
-        "type": BLOCK_TYPE
-      }]);
-      block = new Blockly.Block(workspace, BLOCK_TYPE);
-    });
-
-    assertEquals(BLOCK_TYPE, block.type);
-    assertEquals(
-        'Expecting no warnings when defining and creating a simple block.',
-        warnings.length, 0);
-    // TODO: asserts
-  } finally {
-    block.dispose();
-    workspace.dispose();
-    delete Blockly.Blocks[BLOCK_TYPE];
-  }
-}
-
-/**
- * Ensure a block without a type id fails with a warning, but does not block
- * later definitions.
- */
-function test_json_nullOrUndefinedBlockTypeId() {
-  var BLOCK_TYPE1 = 'test_json_before_bad_blocks';
-  var BLOCK_TYPE2 = 'test_json_after_bad_blocks';
-
-  assertUndefined(Blockly.Blocks[BLOCK_TYPE1]);
-  assertUndefined(Blockly.Blocks[BLOCK_TYPE2]);
-  var blockTypeCount = Object.keys(Blockly.Blocks).length;
-
-  try {
-    var warnings = captureWarnings(function() {
-      Blockly.defineBlocksWithJsonArray([
-          {"type": BLOCK_TYPE1},
-          {"type": undefined},
-          {"type": null},
-          {"type": BLOCK_TYPE2}]);
-    });
-
-    assertNotNullNorUndefined('Block before bad blocks should be defined.',
-        Blockly.Blocks[BLOCK_TYPE1]);
-    assertNotNullNorUndefined('Block after bad blocks should be defined.',
-        Blockly.Blocks[BLOCK_TYPE2]);
-    assertEquals(Object.keys(Blockly.Blocks).length, blockTypeCount + 2);
-    assertEquals(
-        'Expecting 2 warnings, one for each bad block.', warnings.length, 2);
-  } finally {
-    delete Blockly.Blocks[BLOCK_TYPE1];
-    delete Blockly.Blocks[BLOCK_TYPE2];
-  }
-}
-
-/**  Ensure message0 creates an input.  */
-function test_json_message0() {
-  var BLOCK_TYPE = 'test_json_message0';
-  var MESSAGE0 = 'message0';
-
-  var workspace = new Blockly.Workspace();
-  var block;
-  try {
-    Blockly.defineBlocksWithJsonArray([{
-      "type": BLOCK_TYPE,
-      "message0": MESSAGE0
-    }]);
-
-    block = new Blockly.Block(workspace, BLOCK_TYPE);
-    assertEquals(1, block.inputList.length);
-    assertEquals(1, block.inputList[0].fieldRow.length);
-    var textField = block.inputList[0].fieldRow[0];
-    assertEquals(Blockly.FieldLabel, textField.constructor);
-    assertEquals(MESSAGE0, textField.getText());
-  } finally {
-    block && block.dispose();
-    workspace.dispose();
-    delete Blockly.Blocks[BLOCK_TYPE];
-  }
-}
-
-/**  Ensure message1 creates a new input.  */
-function test_json_message1() {
-  var BLOCK_TYPE = 'test_json_message1';
-  var MESSAGE0 = 'message0';
-  var MESSAGE1 = 'message1';
-
-  var workspace = new Blockly.Workspace();
-  var block;
-  try {
-    Blockly.defineBlocksWithJsonArray([{
-      "type": BLOCK_TYPE,
-      "message0": MESSAGE0,
-      "message1": MESSAGE1
-    }]);
-
-    block = new Blockly.Block(workspace, BLOCK_TYPE);
-    assertEquals(2, block.inputList.length);
-
-    assertEquals(1, block.inputList[0].fieldRow.length);
-    var textField = block.inputList[0].fieldRow[0];
-    assertEquals(Blockly.FieldLabel, textField.constructor);
-    assertEquals(MESSAGE0, textField.getText());
-
-    assertEquals(1, block.inputList[1].fieldRow.length);
-    var textField = block.inputList[1].fieldRow[0];
-    assertEquals(Blockly.FieldLabel, textField.constructor);
-    assertEquals(MESSAGE1, textField.getText());
-  } finally {
-    block && block.dispose();
-    workspace.dispose();
-    delete Blockly.Blocks[BLOCK_TYPE];
-  }
-}
-
-/**  Ensure message string is dereferenced.  */
-function test_json_message0_i18n() {
-  var BLOCK_TYPE = 'test_json_message0_i18n';
-  var MESSAGE0 = '%{BKY_MESSAGE}';
-  var MESSAGE = 'message';
-
-  Blockly.Msg['MESSAGE'] = MESSAGE;
-
-  var workspace = new Blockly.Workspace();
-  var block;
-  try {
-    Blockly.defineBlocksWithJsonArray([{
-      "type": BLOCK_TYPE,
-      "message0": MESSAGE0
-    }]);
-
-    block = new Blockly.Block(workspace, BLOCK_TYPE);
-    assertEquals(1, block.inputList.length);
-    assertEquals(1, block.inputList[0].fieldRow.length);
-    var textField = block.inputList[0].fieldRow[0];
-    assertEquals(Blockly.FieldLabel, textField.constructor);
-    assertEquals(MESSAGE, textField.getText());
-  } finally {
-    block && block.dispose(); // Disposes of textField, too.
-    workspace.dispose();
-    delete Blockly.Blocks[BLOCK_TYPE];
-    delete Blockly.Msg['MESSAGE'];
-  }
-}
-
-function test_json_dropdown() {
-  var BLOCK_TYPE = 'test_json_dropdown';
-  var FIELD_NAME = 'FIELD_NAME';
-  var LABEL0 = 'LABEL0';
-  var VALUE0 = 'VALUE0';
-  var LABEL1 = 'LABEL1';
-  var VALUE1 = 'VALUE1';
-
-  var workspace = new Blockly.Workspace();
-  var block;
-  try {
-    Blockly.defineBlocksWithJsonArray([{
-      "type": BLOCK_TYPE,
-      "message0": "%1",
-      "args0": [
-        {
-          "type": "field_dropdown",
-          "name": FIELD_NAME,
-          "options": [
-            [LABEL0, VALUE0],
-            [LABEL1, VALUE1]
-          ]
-        }
-      ]
-    }]);
-
-    block = new Blockly.Block(workspace, BLOCK_TYPE);
-    assertEquals(1, block.inputList.length);
-    assertEquals(1, block.inputList[0].fieldRow.length);
-    var dropdown = block.inputList[0].fieldRow[0];
-    assertEquals(dropdown, block.getField(FIELD_NAME));
-    assertEquals(Blockly.FieldDropdown, dropdown.constructor);
-    assertEquals(VALUE0, dropdown.getValue());
-
-    var options = dropdown.getOptions();
-    assertEquals(LABEL0, options[0][0]);
-    assertEquals(VALUE0, options[0][1]);
-    assertEquals(LABEL1, options[1][0]);
-    assertEquals(VALUE1, options[1][1]);
-  } finally {
-    block && block.dispose();  // Disposes of dropdown, too.
-    workspace.dispose();
-    delete Blockly.Blocks[BLOCK_TYPE];
-  }
-}
-
-function test_json_dropdown_image() {
-  var BLOCK_TYPE = 'test_json_dropdown';
-  var FIELD_NAME = 'FIELD_NAME';
-  var IMAGE1_ALT_TEXT = 'Localized message.';
-  Blockly.Msg['ALT_TEXT'] = IMAGE1_ALT_TEXT;
-  var IMAGE0 = {
-    'width': 12,
-    'height': 34,
-    'src': 'http://image0.src',
-    'alt': 'IMAGE0 alt text'
-  };
-  var VALUE0 = 'VALUE0';
-  var IMAGE1 = {
-    'width': 56,
-    'height': 78,
-    'src': 'http://image1.src',
-    'alt': '%{BKY_ALT_TEXT}'
-  };
-  var VALUE1 = 'VALUE1';
-  var IMAGE2 = {
-    'width': 90,
-    'height': 123,
-    'src': 'http://image2.src'
-  };
-  var VALUE2 = 'VALUE2';
-
-  var workspace = new Blockly.Workspace();
-  var block;
-  try {
-    Blockly.defineBlocksWithJsonArray([{
-      "type": BLOCK_TYPE,
-      "message0": "%1",
-      "args0": [
-        {
-          "type": "field_dropdown",
-          "name": FIELD_NAME,
-          "options": [
-            [IMAGE0, VALUE0],
-            [IMAGE1, VALUE1],
-            [IMAGE2, VALUE2]
-          ]
-        }
-      ]
-    }]);
-
-    block = new Blockly.Block(workspace, BLOCK_TYPE);
-    assertEquals(1, block.inputList.length);
-    assertEquals(1, block.inputList[0].fieldRow.length);
-    var dropdown = block.inputList[0].fieldRow[0];
-    assertEquals(dropdown, block.getField(FIELD_NAME));
-    assertEquals(Blockly.FieldDropdown, dropdown.constructor);
-    assertEquals(VALUE0, dropdown.getValue());
-
-    var options = dropdown.getOptions();
-    var image0 = options[0][0];
-    assertEquals(IMAGE0.width, image0.width);
-    assertEquals(IMAGE0.height, image0.height);
-    assertEquals(IMAGE0.src, image0.src);
-    assertEquals(IMAGE0.alt, image0.alt);
-    assertEquals(VALUE0, options[0][1]);
-
-    var image1 = options[1][0];
-    assertEquals(IMAGE1.width, image1.width);
-    assertEquals(IMAGE1.height, image1.height);
-    assertEquals(IMAGE1.src, image1.src);
-    assertEquals(IMAGE1.alt, IMAGE1_ALT_TEXT);  // Via Msg reference
-    assertEquals(VALUE1, options[1][1]);
-
-    var image2 = options[2][0];
-    assertEquals(IMAGE2.width, image2.width);
-    assertEquals(IMAGE2.height, image2.height);
-    assertEquals(IMAGE2.src, image2.src);
-    assert(image2.alt == null);  // No alt specified.
-    assertEquals(VALUE2, options[2][1]);
-  } finally {
-    block && block.dispose();  // Disposes of dropdown, too.
-    workspace.dispose();
-    delete Blockly.Blocks[BLOCK_TYPE];
-    delete Blockly.Msg['ALTTEXT'];
-  }
-}
-
-function test_defineBlocksWithJsonArray_nullItem() {
-  var BLOCK_TYPE1 = 'test_block_before_null';
-  var BLOCK_TYPE2 = 'test_block_after_null';
-
-  assertUndefined(Blockly.Blocks[BLOCK_TYPE1]);
-  assertUndefined(Blockly.Blocks[BLOCK_TYPE2]);
-  var blockTypeCount = Object.keys(Blockly.Blocks).length;
-
-  try {
-    var warnings = captureWarnings(function() {
-      Blockly.defineBlocksWithJsonArray([
-          {
-            "type": BLOCK_TYPE1,
-            "message0": 'before'
-          },
-          null,
-          {
-            "type": BLOCK_TYPE2,
-            "message0": 'after'
-          }]);
-    });
-    assertNotNullNorUndefined(
-        'Block before null in array should be defined.',
-        Blockly.Blocks[BLOCK_TYPE1]);
-    assertNotNullNorUndefined(
-        'Block after null in array should be defined.',
-        Blockly.Blocks[BLOCK_TYPE2]);
-    assertEquals(Object.keys(Blockly.Blocks).length, blockTypeCount + 2);
-    assertEquals('Expected 1 warning for the bad block.', warnings.length, 1);
-  } finally {
-    workspace.dispose();
-    delete Blockly.Blocks[BLOCK_TYPE1];
-    delete Blockly.Blocks[BLOCK_TYPE2];
-  }
-}
-
-function test_defineBlocksWithJsonArray_undefinedItem() {
-  var BLOCK_TYPE1 = 'test_block_before_undefined';
-  var BLOCK_TYPE2 = 'test_block_after_undefined';
-
-  assertUndefined(Blockly.Blocks[BLOCK_TYPE1]);
-  assertUndefined(Blockly.Blocks[BLOCK_TYPE2]);
-  var blockTypeCount = Object.keys(Blockly.Blocks).length;
-
-  try {
-    var warnings = captureWarnings(function() {
-      Blockly.defineBlocksWithJsonArray([
-          {
-            "type": BLOCK_TYPE1,
-            "message0": 'before'
-          },
-          undefined,
-          {
-            "type": BLOCK_TYPE2,
-            "message0": 'after'
-          }]);
-    });
-    assertNotNullNorUndefined(
-        'Block before undefined in array should be defined.',
-        Blockly.Blocks[BLOCK_TYPE1]);
-    assertNotNullNorUndefined(
-        'Block after undefined in array should be defined.',
-        Blockly.Blocks[BLOCK_TYPE2]);
-    assertEquals(Object.keys(Blockly.Blocks).length, blockTypeCount + 2);
-    assertEquals('Expected 1 warning for the bad block.', warnings.length, 1);
-  } finally {
-    workspace.dispose();
-    delete Blockly.Blocks[BLOCK_TYPE1];
-    delete Blockly.Blocks[BLOCK_TYPE2];
-  }
-}
diff --git a/tests/mocha/.eslintrc.json b/tests/mocha/.eslintrc.json
index 48d7af0e7..c6ae36484 100644
--- a/tests/mocha/.eslintrc.json
+++ b/tests/mocha/.eslintrc.json
@@ -6,6 +6,7 @@
     "globals": {
         "chai": false,
         "sinon": false,
+        "assert": true,
         "assertArrayEquals": true,
         "assertNull": true,
         "assertNotNull": true,
@@ -15,6 +16,7 @@
         "isEqualArrays": true,
         "assertUndefined": true,
         "assertNotUndefined": true,
+        "assertNotNullNorUndefined": true,
         "defineStackBlock": true,
         "defineRowBlock": true,
         "defineStatementBlock": true,
diff --git a/tests/mocha/index.html b/tests/mocha/index.html
index f535ba2e1..ee645b79e 100644
--- a/tests/mocha/index.html
+++ b/tests/mocha/index.html
@@ -48,6 +48,7 @@
     <script src="field_variable_test.js"></script>
     <script src="gesture_test.js"></script>
     <script src="input_test.js"></script>
+    <script src="json_test.js"></script>
     <script src="key_map_test.js"></script>
     <script src="metrics_test.js"></script>
     <script src="names_test.js"></script>
diff --git a/tests/mocha/json_test.js b/tests/mocha/json_test.js
new file mode 100644
index 000000000..b6b79123b
--- /dev/null
+++ b/tests/mocha/json_test.js
@@ -0,0 +1,343 @@
+/**
+ * @license
+ * Copyright 2020 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+suite('JSON Block Definitions', function() {
+  setup(function() {
+    this.workspace_ = new Blockly.Workspace();
+    this.blocks_ = [];
+    this.blockTypes_ = [];
+    this.messages_ = [];
+  });
+
+  teardown(function() {
+    for (var i = 0; i < this.blocks_.length; i++) {
+      var block = this.blocks_[i];
+      block.dispose();
+    }
+    for (var i = 0, blockType; (blockType = this.blockTypes_[i]); i++) {
+      delete Blockly.Blocks[blockType];
+    }
+    for (var i = 0, message; (message = this.messages_[i]); i++) {
+      delete Blockly.Msg[message];
+    }
+    this.workspace_.dispose();
+  });
+
+  /**
+   * Captures the strings sent to console.warn() when calling a function.
+   * @param {function} innerFunc The function where warnings may called.
+   * @return {string[]} The warning messages (only the first arguments).
+   */
+  function captureWarnings(innerFunc) {
+    var msgs = [];
+    var nativeConsoleWarn = console.warn;
+    try {
+      console.warn = function(msg) {
+        msgs.push(msg);
+        nativeConsoleWarn.apply(console, arguments);
+      };
+      innerFunc();
+    } finally {
+      console.warn = nativeConsoleWarn;
+    }
+    return msgs;
+  }
+
+  suite('defineBlocksWithJsonArray', function() {
+    test('Basic block', function() {
+      /**  Ensure a block can be instantiated from a JSON definition.  */
+      var BLOCK_TYPE = 'test_json_minimal';
+      this.blockTypes_.push(BLOCK_TYPE);
+      var workspace = this.workspace_;
+      var block;
+      var warnings = captureWarnings(function() {
+        Blockly.defineBlocksWithJsonArray([{
+          "type": BLOCK_TYPE
+        }]);
+        block = new Blockly.Block(workspace, BLOCK_TYPE);
+      });
+      this.blocks_.push(block);
+
+      assertNotNull(block);
+      assertEquals(BLOCK_TYPE, block.type);
+      assertEquals(
+          'Expecting no warnings when defining and creating a simple block.',
+          warnings.length, 0);
+    });
+
+    test('Null or undefined type id', function() {
+      var BLOCK_TYPE1 = 'test_json_before_bad_blocks';
+      var BLOCK_TYPE2 = 'test_json_after_bad_blocks';
+      this.blockTypes_.push(BLOCK_TYPE1);
+      this.blockTypes_.push(BLOCK_TYPE2);
+
+      assertUndefined(Blockly.Blocks[BLOCK_TYPE1]);
+      assertUndefined(Blockly.Blocks[BLOCK_TYPE2]);
+      var blockTypeCount = Object.keys(Blockly.Blocks).length;
+
+      var warnings = captureWarnings(function() {
+        Blockly.defineBlocksWithJsonArray([
+          {"type": BLOCK_TYPE1},
+          {"type": undefined},
+          {"type": null},
+          {"type": BLOCK_TYPE2}]);
+      });
+
+      assertNotNullNorUndefined('Block before bad blocks should be defined.',
+          Blockly.Blocks[BLOCK_TYPE1]);
+      assertNotNullNorUndefined('Block after bad blocks should be defined.',
+          Blockly.Blocks[BLOCK_TYPE2]);
+      assertEquals(Object.keys(Blockly.Blocks).length, blockTypeCount + 2);
+      assertEquals(
+          'Expecting 2 warnings, one for each bad block.', warnings.length, 2);
+    });
+
+    test('Null item', function() {
+      var BLOCK_TYPE1 = 'test_block_before_null';
+      var BLOCK_TYPE2 = 'test_block_after_null';
+      this.blockTypes_.push(BLOCK_TYPE1);
+      this.blockTypes_.push(BLOCK_TYPE2);
+
+      assertUndefined(Blockly.Blocks[BLOCK_TYPE1]);
+      assertUndefined(Blockly.Blocks[BLOCK_TYPE2]);
+      var blockTypeCount = Object.keys(Blockly.Blocks).length;
+
+      var warnings = captureWarnings(function() {
+        Blockly.defineBlocksWithJsonArray([
+          {
+            "type": BLOCK_TYPE1,
+            "message0": 'before'
+          },
+          null,
+          {
+            "type": BLOCK_TYPE2,
+            "message0": 'after'
+          }]);
+      });
+      assertNotNullNorUndefined(
+          'Block before null in array should be defined.',
+          Blockly.Blocks[BLOCK_TYPE1]);
+      assertNotNullNorUndefined(
+          'Block after null in array should be defined.',
+          Blockly.Blocks[BLOCK_TYPE2]);
+      assertEquals(Object.keys(Blockly.Blocks).length, blockTypeCount + 2);
+      assertEquals('Expected 1 warning for the bad block.', warnings.length, 1);
+    });
+
+    test('Undefined item', function() {
+      var BLOCK_TYPE1 = 'test_block_before_undefined';
+      var BLOCK_TYPE2 = 'test_block_after_undefined';
+      this.blockTypes_.push(BLOCK_TYPE1);
+      this.blockTypes_.push(BLOCK_TYPE2);
+
+      assertUndefined(Blockly.Blocks[BLOCK_TYPE1]);
+      assertUndefined(Blockly.Blocks[BLOCK_TYPE2]);
+      var blockTypeCount = Object.keys(Blockly.Blocks).length;
+      var warnings = captureWarnings(function() {
+        Blockly.defineBlocksWithJsonArray([
+          {
+            "type": BLOCK_TYPE1,
+            "message0": 'before'
+          },
+          undefined,
+          {
+            "type": BLOCK_TYPE2,
+            "message0": 'after'
+          }]);
+      });
+      assertNotNullNorUndefined(
+          'Block before undefined in array should be defined.',
+          Blockly.Blocks[BLOCK_TYPE1]);
+      assertNotNullNorUndefined(
+          'Block after undefined in array should be defined.',
+          Blockly.Blocks[BLOCK_TYPE2]);
+      assertEquals(Object.keys(Blockly.Blocks).length, blockTypeCount + 2);
+      assertEquals('Expected 1 warning for the bad block.', warnings.length, 1);
+    });
+
+    test('message0 creates input', function() {
+      var BLOCK_TYPE = 'test_json_message0';
+      this.blockTypes_.push(BLOCK_TYPE);
+      var MESSAGE0 = 'message0';
+      Blockly.defineBlocksWithJsonArray([{
+        "type": BLOCK_TYPE,
+        "message0": MESSAGE0
+      }]);
+
+      var block = new Blockly.Block(this.workspace_, BLOCK_TYPE);
+      assertEquals(1, block.inputList.length);
+      assertEquals(1, block.inputList[0].fieldRow.length);
+      var textField = block.inputList[0].fieldRow[0];
+      assertEquals(Blockly.FieldLabel, textField.constructor);
+      assertEquals(MESSAGE0, textField.getText());
+    });
+
+    test('message1 and message0 creates two inputs', function() {
+      /**  Ensure message1 creates a new input.  */
+      var BLOCK_TYPE = 'test_json_message1';
+      this.blockTypes_.push(BLOCK_TYPE);
+      var MESSAGE0 = 'message0';
+      var MESSAGE1 = 'message1';
+      Blockly.defineBlocksWithJsonArray([{
+        "type": BLOCK_TYPE,
+        "message0": MESSAGE0,
+        "message1": MESSAGE1
+      }]);
+
+      var block = new Blockly.Block(this.workspace_, BLOCK_TYPE);
+      this.blocks_.push(block);
+      assertEquals(2, block.inputList.length);
+
+      assertEquals(1, block.inputList[0].fieldRow.length);
+      var textField = block.inputList[0].fieldRow[0];
+      assertEquals(Blockly.FieldLabel, textField.constructor);
+      assertEquals(MESSAGE0, textField.getText());
+
+      assertEquals(1, block.inputList[1].fieldRow.length);
+      var textField = block.inputList[1].fieldRow[0];
+      assertEquals(Blockly.FieldLabel, textField.constructor);
+      assertEquals(MESSAGE1, textField.getText());
+    });
+
+    test('Message string is dereferenced', function() {
+      var BLOCK_TYPE = 'test_json_message0_i18n';
+      this.blockTypes_.push(BLOCK_TYPE);
+      var MESSAGE0 = '%{BKY_MESSAGE}';
+      var MESSAGE = 'message';
+
+      Blockly.Msg['MESSAGE'] = MESSAGE;
+      this.messages_.push('MESSAGE');
+      Blockly.defineBlocksWithJsonArray([{
+        "type": BLOCK_TYPE,
+        "message0": MESSAGE0
+      }]);
+
+      var block = new Blockly.Block(this.workspace_, BLOCK_TYPE);
+      this.blocks_.push(block);
+      assertEquals(1, block.inputList.length);
+      assertEquals(1, block.inputList[0].fieldRow.length);
+      var textField = block.inputList[0].fieldRow[0];
+      assertEquals(Blockly.FieldLabel, textField.constructor);
+      assertEquals(MESSAGE, textField.getText());
+    });
+
+    test('Dropdown', function() {
+      var BLOCK_TYPE = 'test_json_dropdown';
+      this.blockTypes_.push(BLOCK_TYPE);
+      var FIELD_NAME = 'FIELD_NAME';
+      var LABEL0 = 'LABEL0';
+      var VALUE0 = 'VALUE0';
+      var LABEL1 = 'LABEL1';
+      var VALUE1 = 'VALUE1';
+      Blockly.defineBlocksWithJsonArray([{
+        "type": BLOCK_TYPE,
+        "message0": "%1",
+        "args0": [
+          {
+            "type": "field_dropdown",
+            "name": FIELD_NAME,
+            "options": [
+              [LABEL0, VALUE0],
+              [LABEL1, VALUE1]
+            ]
+          }
+        ]
+      }]);
+
+      var block = new Blockly.Block(this.workspace_, BLOCK_TYPE);
+      this.blocks_.push(block);
+      assertEquals(1, block.inputList.length);
+      assertEquals(1, block.inputList[0].fieldRow.length);
+      var dropdown = block.inputList[0].fieldRow[0];
+      assertEquals(dropdown, block.getField(FIELD_NAME));
+      assertEquals(Blockly.FieldDropdown, dropdown.constructor);
+      assertEquals(VALUE0, dropdown.getValue());
+
+      var options = dropdown.getOptions();
+      assertEquals(LABEL0, options[0][0]);
+      assertEquals(VALUE0, options[0][1]);
+      assertEquals(LABEL1, options[1][0]);
+      assertEquals(VALUE1, options[1][1]);
+    });
+
+
+    test('Dropdown with images', function() {
+      var BLOCK_TYPE = 'test_json_dropdown';
+      this.blockTypes_.push(BLOCK_TYPE);
+      var FIELD_NAME = 'FIELD_NAME';
+      var IMAGE1_ALT_TEXT = 'Localized message.';
+      Blockly.Msg['ALT_TEXT'] = IMAGE1_ALT_TEXT;
+      this.messages_.push('ALT_TEXT');
+      var IMAGE0 = {
+        'width': 12,
+        'height': 34,
+        'src': 'http://image0.src',
+        'alt': 'IMAGE0 alt text'
+      };
+      var VALUE0 = 'VALUE0';
+      var IMAGE1 = {
+        'width': 56,
+        'height': 78,
+        'src': 'http://image1.src',
+        'alt': '%{BKY_ALT_TEXT}'
+      };
+      var VALUE1 = 'VALUE1';
+      var IMAGE2 = {
+        'width': 90,
+        'height': 123,
+        'src': 'http://image2.src'
+      };
+      var VALUE2 = 'VALUE2';
+
+      Blockly.defineBlocksWithJsonArray([{
+        "type": BLOCK_TYPE,
+        "message0": "%1",
+        "args0": [
+          {
+            "type": "field_dropdown",
+            "name": FIELD_NAME,
+            "options": [
+              [IMAGE0, VALUE0],
+              [IMAGE1, VALUE1],
+              [IMAGE2, VALUE2]
+            ]
+          }
+        ]
+      }]);
+
+      var block = new Blockly.Block(this.workspace_, BLOCK_TYPE);
+      this.blocks_.push(block);
+      assertEquals(1, block.inputList.length);
+      assertEquals(1, block.inputList[0].fieldRow.length);
+      var dropdown = block.inputList[0].fieldRow[0];
+      assertEquals(dropdown, block.getField(FIELD_NAME));
+      assertEquals(Blockly.FieldDropdown, dropdown.constructor);
+      assertEquals(VALUE0, dropdown.getValue());
+
+      function assertImageEquals(actualImage, expectedImage) {
+        assertEquals(actualImage.width, expectedImage.width);
+        assertEquals(actualImage.height, expectedImage.height);
+        assertEquals(actualImage.src, expectedImage.src);
+      }
+
+      var options = dropdown.getOptions();
+      var image0 = options[0][0];
+      assertImageEquals(IMAGE0, image0);
+      assertEquals(IMAGE0.alt, image0.alt);
+      assertEquals(options[0][1], VALUE0);
+
+      var image1 = options[1][0];
+      assertImageEquals(IMAGE1, image1);
+      assertEquals(IMAGE1.alt, IMAGE1_ALT_TEXT);  // Via Msg reference
+      assertEquals(VALUE1, options[1][1]);
+
+      var image2 = options[2][0];
+      assertImageEquals(IMAGE1, image1);
+      assert(image2.alt == null);  // No alt specified.
+      assertEquals(VALUE2, options[2][1]);
+    });
+  });
+});