Add a test and fix for not serializing top-level variable reporters

src/serialization/sb3.js

@@ -325,7 +325,7 @@ const serializeBlocks = function (blocks) {
         // a shadow block, and there are no blocks that reference it, otherwise
         // they would have been compressed in the last pass)
         if (Array.isArray(serializedBlock) &&
-            [VAR_PRIMITIVE, LIST_PRIMITIVE].indexOf(serializedBlock) < 0) {
+            [VAR_PRIMITIVE, LIST_PRIMITIVE].indexOf(serializedBlock[0]) < 0) {
             log.warn(`Found an unexpected top level primitive with block ID: ${
                 blockID}; deleting it from serialized blocks.`);
             delete obj[blockID];

test/unit/serialization_sb3.js

@@ -7,6 +7,7 @@ const exampleProjectPath = path.resolve(__dirname, '../fixtures/clone-cleanup.sb
 const commentsSB2ProjectPath = path.resolve(__dirname, '../fixtures/comments.sb2');
 const commentsSB3ProjectPath = path.resolve(__dirname, '../fixtures/comments.sb3');
 const commentsSB3NoDupeIds = path.resolve(__dirname, '../fixtures/comments_no_duplicate_id_serialization.sb3');
+const variableReporterSB2ProjectPath = path.resolve(__dirname, '../fixtures/top-level-variable-reporter.sb2');
 const FakeRenderer = require('../fixtures/fake-renderer');
 
 test('serialize', t => {
@@ -236,3 +237,16 @@ test('getExtensionIdForOpcode', t => {
 
     t.end();
 });
+
+test('(#1608) serializeBlocks maintains top level variable reporters', t => {
+    const vm = new VirtualMachine();
+    vm.loadProject(readFileToBuffer(variableReporterSB2ProjectPath))
+        .then(() => {
+            const blocks = vm.runtime.targets[0].blocks._blocks;
+            const result = sb3.serialize(vm.runtime).targets[0].blocks;
+            // Project should have 1 block, a top-level variable reporter
+            t.equal(Object.keys(blocks).length, 1);
+            t.equal(Object.keys(result).length, 1);
+            t.end();
+        });
+});