diff --git a/packages/db/src/engines/MemoryDb.spec.ts b/packages/db/src/engines/MemoryDb.spec.ts
new file mode 100644
index 000000000..dfb9ed89c
--- /dev/null
+++ b/packages/db/src/engines/MemoryDb.spec.ts
@@ -0,0 +1,27 @@
+// Copyright 2017-2019 @polkadot/db authors & contributors
+// This software may be modified and distributed under the terms
+// of the Apache-2.0 license. See the LICENSE file for details.
+
+import MemoryDb from './MemoryDb';
+
+describe('MemoryDb', () => {
+  const memory = new MemoryDb();
+
+  it('gets the combioned size of the entry values', () => {
+    memory.put(new Uint8Array([1]), new Uint8Array([1, 2, 3]));
+    memory.put(new Uint8Array([2]), new Uint8Array([1, 2, 3]));
+    memory.put(new Uint8Array([3]), new Uint8Array([1, 2, 3]));
+
+    expect(memory.size()).toEqual(9);
+  });
+
+  it('does not throw on the stubs', (done) => {
+    memory.close();
+    memory.open();
+    memory.drop();
+    memory.empty();
+    memory.rename('foo', 'bar');
+
+    memory.maintain(() => done());
+  });
+});
diff --git a/packages/util/src/compact/toU8a.spec.ts b/packages/util/src/compact/toU8a.spec.ts
index 3e9b26f2a..75da1ab4c 100644
--- a/packages/util/src/compact/toU8a.spec.ts
+++ b/packages/util/src/compact/toU8a.spec.ts
@@ -39,6 +39,14 @@ describe('encode', () => {
     );
   });
 
+  it('encodes basic u32 values (< 2^30)', () => {
+    expect(
+      compactToU8a(0x1fff)
+    ).toEqual(
+      new Uint8Array([253, 127])
+    );
+  });
+
   it('encodes basic u32 values (short)', () => {
     expect(
       compactToU8a(0xffff)
diff --git a/packages/util/src/polyfill/fill.spec.ts b/packages/util/src/polyfill/fill.spec.ts
index 21cdce74d..2378f60f9 100644
--- a/packages/util/src/polyfill/fill.spec.ts
+++ b/packages/util/src/polyfill/fill.spec.ts
@@ -4,19 +4,31 @@
 
 describe('Array.fill', () => {
   let arrayFill: any;
+  let u8aFill: any;
 
   beforeEach(() => {
     arrayFill = Array.prototype.fill;
-    Array.prototype.fill = null as any;
+    u8aFill = Uint8Array.prototype.fill;
+
+    // @ts-ignore
+    Array.prototype.fill = null;
+    // @ts-ignore
+    Uint8Array.prototype.fill = null;
 
     require('./fill');
   });
 
   afterEach(() => {
     Array.prototype.fill = arrayFill;
+    Uint8Array.prototype.fill = u8aFill;
   });
 
   it('uses the polyfills', () => {
-    expect([1, 2, 3, 4, 5, 6, 7, 8].fill(5, 3)).toEqual([1, 2, 3, 5, 5, 5, 5, 5]);
+    expect(
+      [1, 2, 3, 4, 5, 6, 7, 8].fill(5, 3)
+    ).toEqual([1, 2, 3, 5, 5, 5, 5, 5]);
+    expect(
+      new Uint8Array([1, 2, 3, 4, 5, 6, 7, 8]).fill(5, 3)
+    ).toEqual(new Uint8Array([1, 2, 3, 5, 5, 5, 5, 5]));
   });
 });
diff --git a/packages/util/src/polyfill/setPrototypeOf.spec.ts b/packages/util/src/polyfill/setPrototypeOf.spec.ts
new file mode 100644
index 000000000..e483896eb
--- /dev/null
+++ b/packages/util/src/polyfill/setPrototypeOf.spec.ts
@@ -0,0 +1,27 @@
+// Copyright 2017-2019 @polkadot/util authors & contributors
+// This software may be modified and distributed under the terms
+// of the Apache-2.0 license. See the LICENSE file for details.
+
+describe('setPrototypeOf', () => {
+  let orig: (o: any, proto: object | null) => any;
+
+  beforeEach(() => {
+    orig = Object.setPrototypeOf;
+
+    // @ts-ignore
+    Object.setPrototypeOf = null;
+
+    require('./setPrototypeOf');
+  });
+
+  afterEach(() => {
+    Object.setPrototypeOf = orig;
+  });
+
+  it('polyfills with no exceptions', () => {
+    const obj = {};
+    const proto = { foo: 'bar' };
+
+    expect(Object.setPrototypeOf(obj, proto).__proto__).toBe(proto);
+  });
+});