diff --git a/package.json b/package.json
index cd1760c9..c7f1ef7c 100644
--- a/package.json
+++ b/package.json
@@ -57,7 +57,8 @@
     "bundlesize": "~0.18.0",
     "chai": "^4.2.0",
     "chai-string": "^1.5.0",
-    "dirty-chai": "^2.0.1"
+    "dirty-chai": "^2.0.1",
+    "sinon": "^7.3.2"
   },
   "engines": {
     "node": ">=10.0.0",
diff --git a/test/keys/secp256k1.spec.js b/test/keys/secp256k1.spec.js
index 60af5d90..a40de231 100644
--- a/test/keys/secp256k1.spec.js
+++ b/test/keys/secp256k1.spec.js
@@ -5,34 +5,19 @@ const chai = require('chai')
 const dirtyChai = require('dirty-chai')
 const expect = chai.expect
 chai.use(dirtyChai)
+const sinon = require('sinon')
+
 const fixtures = require('../fixtures/secp256k1')
 const crypto = require('../../src')
 
-const mockPublicKey = {
-  bytes: fixtures.pbmPublicKey
-}
-
-const mockPrivateKey = {
-  bytes: fixtures.pbmPrivateKey,
-  public: mockPublicKey
-}
-
-const mockSecp256k1Module = {
-  generateKeyPair (bits) {
-    return mockPrivateKey
-  },
-
-  unmarshalSecp256k1PrivateKey (buf) {
-    return mockPrivateKey
-  },
-
-  unmarshalSecp256k1PublicKey (buf) {
-    return mockPublicKey
-  }
-}
-
 describe('without libp2p-crypto-secp256k1 module present', () => {
-  crypto.keys.supportedKeys.secp256k1 = undefined
+  before(() => {
+    sinon.replace(crypto.keys.supportedKeys, 'secp256k1', null)
+  })
+
+  after(() => {
+    sinon.restore()
+  })
 
   it('fails to generate a secp256k1 key', async () => {
     try {
@@ -60,22 +45,15 @@ describe('without libp2p-crypto-secp256k1 module present', () => {
 })
 
 describe('with libp2p-crypto-secp256k1 module present', () => {
-  let key
-
-  before(async () => {
-    crypto.keys.supportedKeys.secp256k1 = mockSecp256k1Module
-    key = await crypto.keys.generateKeyPair('secp256k1', 256)
-  })
-
-  after(() => {
-    delete crypto.keys.secp256k1
-  })
-
-  it('generates a valid key', () => {
+  it('generates a valid key', async () => {
+    const key = await crypto.keys.generateKeyPair('secp256k1', 256)
     expect(key).to.exist()
   })
 
   it('protobuf encoding', async () => {
+    const key = await crypto.keys.generateKeyPair('secp256k1', 256)
+    expect(key).to.exist()
+
     const keyMarshal = crypto.keys.marshalPrivateKey(key)
     const key2 = await crypto.keys.unmarshalPrivateKey(keyMarshal)
     const keyMarshal2 = crypto.keys.marshalPrivateKey(key2)
@@ -89,4 +67,14 @@ describe('with libp2p-crypto-secp256k1 module present', () => {
 
     expect(pkMarshal).to.eql(pkMarshal2)
   })
+
+  it('unmarshals a secp256k1 private key', async () => {
+    const key = await crypto.keys.unmarshalPrivateKey(fixtures.pbmPrivateKey)
+    expect(key).to.exist()
+  })
+
+  it('unmarshals a secp256k1 public key', () => {
+    const key = crypto.keys.unmarshalPublicKey(fixtures.pbmPublicKey)
+    expect(key).to.exist()
+  })
 })