diff --git a/js/tests/block-chain_test.js b/js/tests/block-chain_test.js
new file mode 100644
index 00000000..59e5973a
--- /dev/null
+++ b/js/tests/block-chain_test.js
@@ -0,0 +1,54 @@
+export const tests = []
+const t = (f) => tests.push(f)
+
+t(({ eq }) => {
+  const { chain, ...block } = blockChain({ a: 1 })
+  return eq(block, {
+    index: 1,
+    data: { a: 1 },
+    prev: { index: 0, hash: '0' },
+    hash: '1103f27',
+  })
+})
+
+t(({ eq }) => {
+  const block = blockChain({ a: 1 }).chain({ hello: 'world' })
+
+  const chain = block
+    .chain({ value: 4455 })
+    .chain({ some: 'data' })
+    .chain({ cool: 'stuff' })
+
+  const fork = block
+    .chain({ value: 335 })
+    .chain({ some: 'data' })
+    .chain({ cool: 'stuff' })
+
+  return eq(
+    {
+      chainRoot: chain.prev.prev.prev,
+      forkRoot: chain.prev.prev.prev,
+      chainHash: chain.hash,
+      forkHash: fork.hash,
+      index: chain.index,
+      data: chain.data,
+    },
+    {
+      chainRoot: block,
+      forkRoot: block,
+      chainHash: '1qr3qfs',
+      forkHash: '1x9gsc1',
+      index: fork.index,
+      data: fork.data,
+    },
+  )
+})
+
+t(({ eq }) => {
+  const random = Math.random()
+  const hash = hashCode(`21103f27{"random":${random}}`)
+  const { prev, chain, ...block } = blockChain({ a: 1 }).chain({ random })
+  return eq(block, { index: 2, data: { random }, hash })
+})
+
+Object.freeze(tests)
diff --git a/js/tests/collections_test.js b/js/tests/collections_test.js
new file mode 100644
index 00000000..5a7a4f2c
--- /dev/null
+++ b/js/tests/collections_test.js
@@ -0,0 +1,59 @@
+export const tests = []
+const t = f => tests.push(f)
+
+t(({ eq, ctx }) => eq(arrToSet([1, ctx, ctx, 3, 3]), new Set([1, ctx, 3])))
+t(({ eq, ctx }) => eq(arrToStr([1, ctx, ctx, 3]), `${1}${ctx}${ctx}${3}`))
+t(({ eq, ctx }) => eq(setToArr(new Set([1, ctx, 3])), [1, ctx, 3]))
+t(({ eq, ctx }) => eq(setToStr(new Set([1, ctx, 3])), `${1}${ctx}${3}`))
+t(({ eq, ctx }) => eq(strToArr(`${1}${ctx}${3}`), ['1', ...ctx, '3']))
+
+t(({ eq, ctx }) =>
+  eq(strToSet(`12${ctx[0]}23`), new Set(['1', '2', ctx[0], '3'])),
+)
+
+t(({ eq, ctx }) =>
+  eq(
+    mapToObj(
+      new Map([
+        [ctx, ctx],
+        ['a', 2],
+      ]),
+    ),
+    { [ctx]: ctx, a: 2 },
+  ),
+)
+
+t(({ eq, ctx }) => eq(objToArr({ a: 1, b: ctx }), [1, ctx]))
+
+t(({ eq, ctx }) =>
+  eq(
+    objToMap({ [ctx]: ctx, a: 2 }),
+    new Map([
+      [ctx, ctx],
+      ['a', 2],
+    ]),
+  ),
+)
+
+t(({ eq, ctx }) =>
+  eq(arrToObj([1, ctx, 'pouet']), { '0': 1, '1': ctx, '2': 'pouet' }),
+)
+
+t(({ eq, ctx }) =>
+  eq(strToObj(`2${ctx[0]}2`), { '0': '2', '1': ctx[0], '2': '2' }),
+)
+
+t(({ eq }) => eq(superTypeOf(new Map()), 'Map'))
+t(({ eq }) => eq(superTypeOf(new Set()), 'Set'))
+t(({ eq }) => eq(superTypeOf({}), 'Object'))
+t(({ eq }) => eq(superTypeOf(''), 'String'))
+t(({ eq }) => eq(superTypeOf(666), 'Number'))
+t(({ eq }) => eq(superTypeOf(NaN), 'Number'))
+t(({ eq }) => eq(superTypeOf([]), 'Array'))
+t(({ eq }) => eq(superTypeOf(null), 'null'))
+t(({ eq }) => eq(superTypeOf(undefined), 'undefined'))
+t(({ eq }) => eq(superTypeOf(superTypeOf), 'Function'))
+
+export const setup = () => Math.random().toString(36).slice(2)
+
+Object.freeze(tests)