diff --git a/implementations/javascript/packages/schema/test/checker.test.ts b/implementations/javascript/packages/schema/test/checker.test.ts
index 6db9926..6deb73d 100644
--- a/implementations/javascript/packages/schema/test/checker.test.ts
+++ b/implementations/javascript/packages/schema/test/checker.test.ts
@@ -16,6 +16,9 @@ describe('checker', () => {
         it('detects non-bijection for symbol field', () => {
             expect(() => readSchema('version 1 . A = <a @x string symbol> .')).toThrow(/item 1 of fields of A/);
         });
+        it('is OK with no names in simple seqof', () => {
+            expect(readSchema('version 1 . A = [string ...].')).not.toBeNull();
+        });
     });
 
     describe('extensible record', () => {
@@ -38,4 +41,23 @@ describe('checker', () => {
                 .toThrow(/tail of fields of ExtensibleRecord/);
         });
     });
+
+    describe('duplicate bindings', () => {
+        it('complains about duplicates in tuples', () => {
+            expect(() => readSchema('version 1 . A = [@a string @a string].'))
+                .toThrow(/duplicate binding named "a" in item 1 of A/);
+        });
+        it('complains about duplicates in dicts', () => {
+            expect(() => readSchema('version 1 . A = { x: @a string , y: @a string }.'))
+                .toThrow(/duplicate binding named "a" in entry y in dictionary in A/);
+        });
+        it('complains about duplicates in tuple*s', () => {
+            expect(() => readSchema('version 1 . A = [@a string @b string @a int @rest any ...].'))
+                .toThrow(/duplicate binding named "a" in item 2 of A/);
+        });
+        it('complains about duplicates in tuple* tails', () => {
+            expect(() => readSchema('version 1 . A = [@a string @b string @c int @a any ...].'))
+                .toThrow(/duplicate binding named "a" in tail of A/);
+        });
+    });
 });