fix: Fix serialization of the lists_split block.

blocks/lists.ts

@@ -1046,22 +1046,19 @@ blocks['lists_split'] = {
 
   /**
    * Returns the state of this block as a JSON serializable object.
-   * This block does not need to serialize any specific state as it is already
-   * encoded in the dropdown values, but must have an implementation to avoid
-   * the backward compatible XML mutations being serialized.
    *
    * @returns The state of this block.
    */
-  saveExtraState: function (this: SplitBlock): null {
-    return null;
+  saveExtraState: function (this: SplitBlock): {mode: string} {
+    return {'mode': this.getFieldValue('MODE')};
   },
 
   /**
    * Applies the given state to this block.
-   * No extra state is needed or expected as it is already encoded in the
-   * dropdown values.
    */
-  loadExtraState: function (this: SplitBlock) {},
+  loadExtraState: function (this: SplitBlock, state: {mode: string}) {
+    this.updateType_(state['mode']);
+  },
 };
 
 // Register provided blocks.

tests/mocha/blocks/lists_test.js

@@ -181,16 +181,58 @@ suite('Lists', function () {
      * Test cases for serialization tests.
      * @type {Array<SerializationTestCase>}
      */
-    const testCases = makeTestCasesForBlockNotNeedingExtraState_(
+    const testCases = [
       {
-        'type': 'lists_split',
-        'id': '1',
-        'fields': {
-          'MODE': 'SPLIT',
+        title: 'JSON for splitting',
+        json: {
+          type: 'lists_split',
+          id: '1',
+          extraState: {mode: 'SPLIT'},
+          fields: {MODE: 'SPLIT'},
+          inputs: {
+            DELIM: {
+              shadow: {
+                type: 'text',
+                id: '2',
+                fields: {
+                  TEXT: ',',
+                },
+              },
+            },
+          },
+        },
+        assertBlockStructure: (block) => {
+          assert.equal(block.type, 'lists_split');
+          assert.deepEqual(block.outputConnection.getCheck(), ['Array']);
+          assert.isTrue(block.getField('MODE').getValue() === 'SPLIT');
         },
       },
-      '<mutation mode="SPLIT"></mutation>',
-    );
+      {
+        title: 'JSON for joining',
+        json: {
+          type: 'lists_split',
+          id: '1',
+          extraState: {mode: 'JOIN'},
+          fields: {MODE: 'JOIN'},
+          inputs: {
+            DELIM: {
+              shadow: {
+                type: 'text',
+                id: '2',
+                fields: {
+                  TEXT: ',',
+                },
+              },
+            },
+          },
+        },
+        assertBlockStructure: (block) => {
+          assert.equal(block.type, 'lists_split');
+          assert.deepEqual(block.outputConnection.getCheck(), ['String']);
+          assert.isTrue(block.getField('MODE').getValue() === 'JOIN');
+        },
+      },
+    ];
     runSerializationTestSuite(testCases);
   });
 });