diff --git a/lib/github.js b/lib/github.js
index b0f7799..9241093 100644
--- a/lib/github.js
+++ b/lib/github.js
@@ -59,7 +59,7 @@ module.exports.getShas = async function getShas (owner, repo) {
   })
   const headSha = resp.data[0].sha
   const treeSha = resp.data[0].commit.tree.sha
-  return [headSha, treeSha]
+  return { headSha, treeSha }
 }
 
 module.exports.createBlob = async function createBlob (owner, repo, file) {
@@ -117,11 +117,13 @@ module.exports.deleteBranch = async function deleteBranch (owner, repo, branch)
 
 module.exports.getBranch = async function getBranch (owner, repo, branch) {
   try {
-    return await octokit.repos.getBranch({
+    const { data } = await octokit.repos.getBranch({
       owner,
       repo,
       branch
     })
+
+    return data
   } catch (err) {
     if (err.status === 404) {
       return undefined
@@ -166,3 +168,12 @@ module.exports.closePR = async function closePR (owner, repo, pullNumber) {
     state: 'closed'
   })
 }
+
+module.exports.updateRef = async function updateRef (owner, repo, ref, sha) {
+  return octokit.rest.git.updateRef({
+    owner,
+    repo,
+    ref,
+    sha
+  })
+}
diff --git a/lib/test.js b/lib/test.js
index 8d320cd..9d19391 100644
--- a/lib/test.js
+++ b/lib/test.js
@@ -52,14 +52,28 @@ async function pushPatch (dependentPkgJson, dependentOwner, dependentRepo, paren
   const file = JSON.stringify(dependentPkgJson, null, 2) + '\n' // assumes package.json is using two spaces
   const encodedFile = Buffer.from(file).toString('base64')
   const message = `wiby: update ${parentName}`
-  const branch = await context.getTestingBranchName(parentBranchName)
+  const testingBranchName = await context.getTestingBranchName(parentBranchName)
 
-  const [headSha, treeSha] = await github.getShas(dependentOwner, dependentRepo)
+  const testingBranch = await github.getBranch(dependentOwner, dependentRepo, testingBranchName)
   const blobSha = await github.createBlob(dependentOwner, dependentRepo, encodedFile)
-  const newTreeSha = await github.createTree(dependentOwner, dependentRepo, treeSha, blobSha)
-  const commitSha = await github.createCommit(dependentOwner, dependentRepo, message, newTreeSha, headSha)
-  await github.createBranch(dependentOwner, dependentRepo, commitSha, branch)
-  debug(`Changes pushed to https://github.com/${dependentOwner}/${dependentRepo}/blob/${branch}/package.json`)
+
+  if (!testingBranch) {
+    // testing branch does not yet exist - create it
+    const { headSha, treeSha } = await github.getShas(dependentOwner, dependentRepo)
+    const newTreeSha = await github.createTree(dependentOwner, dependentRepo, treeSha, blobSha)
+    const commitSha = await github.createCommit(dependentOwner, dependentRepo, message, newTreeSha, headSha)
+    await github.createBranch(dependentOwner, dependentRepo, commitSha, testingBranchName)
+
+    debug(`Changes pushed to https://github.com/${dependentOwner}/${dependentRepo}/blob/${testingBranchName}/package.json`)
+  } else {
+    // testing branch already exists - ensure we have the package.json patched or at least push an empty commit
+    const { sha: headSha, commit: { tree: { sha: treeSha } } } = testingBranch.commit
+    const newTreeSha = await github.createTree(dependentOwner, dependentRepo, treeSha, blobSha)
+    const commitSha = await github.createCommit(dependentOwner, dependentRepo, message, newTreeSha, headSha)
+    await github.updateRef(dependentOwner, dependentRepo, `heads/${testingBranchName}`, commitSha)
+
+    debug(`Pushed a new commit to https://github.com/${dependentOwner}/${dependentRepo}#${testingBranchName}`)
+  }
 }
 
 const createPR = module.exports.createPR = async function createPR (dependentOwner, dependentRepo, parentBranchName, parentDependencyLink) {
diff --git a/test/cli/test.js b/test/cli/test.js
index 13b4e8d..deb6bd1 100644
--- a/test/cli/test.js
+++ b/test/cli/test.js
@@ -49,6 +49,21 @@ tap.test('test command', async (tap) => {
     tap.match(result, 'Changes pushed to https://github.com/wiby-test/partial/blob/wiby-running-unit-tests/package.json')
   })
 
+  tap.test('test command should update existing wiby test branches', async (tap) => {
+    gitFixture.init('existing-branch')
+
+    const result = childProcess.execSync(`${wibyCommand} test`, {
+      env: {
+        ...process.env,
+        NODE_OPTIONS: `-r ${fixturesPath}/http/test-command-positive.js`
+      }
+    }).toString()
+
+    tap.match(result, 'Pushed a new commit to https://github.com/wiby-test/pass#wiby-existing-branch')
+    tap.match(result, 'Pushed a new commit to https://github.com/wiby-test/fail#wiby-existing-branch')
+    tap.match(result, 'Pushed a new commit to https://github.com/wiby-test/partial#wiby-existing-branch')
+  })
+
   tap.test('test command should not add `wiby-` prefix when branch already has it', async (tap) => {
     gitFixture.init('wiby-running-unit-tests')
 
diff --git a/test/closePR.js b/test/closePR.js
index 60ce13b..ae9fca2 100644
--- a/test/closePR.js
+++ b/test/closePR.js
@@ -41,9 +41,7 @@ tap.test('close PR', (t) => {
       nock('https://api.github.com')
         // get package json
         .patch('/repos/pkgjs/wiby/pulls/1')
-        .reply(200, {
-          data: {}
-        })
+        .reply(200, {})
       const result = await closePR.closeDependencyPR(owner, repo, branch, [{
         status: 'completed',
         conclusion: 'success',
@@ -68,9 +66,7 @@ tap.test('close PR', (t) => {
       // nock setup
       nock('https://api.github.com')
         .get(/repos.*check-runs/)
-        .reply(200, {
-          data: {}
-        })
+        .reply(200, {})
       const result = await closePR({
         dependents: [
           {
diff --git a/test/fixtures/http/clean-command-dry.js b/test/fixtures/http/clean-command-dry.js
index 7d2b1dd..b9329b0 100644
--- a/test/fixtures/http/clean-command-dry.js
+++ b/test/fixtures/http/clean-command-dry.js
@@ -10,7 +10,7 @@ nock.disableNetConnect()
 function nockRepo (nockInstance, repo) {
   return nockInstance
     .get(`/repos/wiby-test/${repo}/branches/wiby-running-unit-tests`)
-    .reply(200)
+    .reply(200, {})
 }
 
 function buildNock () {
diff --git a/test/fixtures/http/clean-command.js b/test/fixtures/http/clean-command.js
index dee62b4..61eeffd 100644
--- a/test/fixtures/http/clean-command.js
+++ b/test/fixtures/http/clean-command.js
@@ -10,7 +10,7 @@ nock.disableNetConnect()
 function nockRepo (nockInstance, repo) {
   return nockInstance
     .get(`/repos/wiby-test/${repo}/branches/wiby-running-unit-tests`)
-    .reply(200)
+    .reply(200, {})
     .delete(`/repos/wiby-test/${repo}/git/refs/heads%2Fwiby-running-unit-tests`)
     .reply(200)
 }
diff --git a/test/fixtures/http/result-command-missing-branch.js b/test/fixtures/http/result-command-missing-branch.js
index 6a0bd50..1c9e89e 100644
--- a/test/fixtures/http/result-command-missing-branch.js
+++ b/test/fixtures/http/result-command-missing-branch.js
@@ -31,7 +31,7 @@ nock('https://api.github.com')
   .get('/repos/wiby-test/pass/branches/wiby-running-unit-tests')
   .reply(200, {})
   .get('/repos/wiby-test/fail/branches/wiby-running-unit-tests')
-  .reply(404, {})
+  .reply(404)
   // get check results
   .get('/repos/wiby-test/fakeRepo/commits/wiby-running-unit-tests/check-runs')
   .reply(200, {
diff --git a/test/fixtures/http/test-command-positive.js b/test/fixtures/http/test-command-positive.js
index 6ca4f01..ddbd09e 100644
--- a/test/fixtures/http/test-command-positive.js
+++ b/test/fixtures/http/test-command-positive.js
@@ -49,7 +49,7 @@ function nockPkgjsWiby (nockInstance) {
       }
     ])
     .get('/repos/wiby-test/pass/branches/wiby-running-unit-tests')
-    .reply(404, {})
+    .reply(404)
 }
 
 function nockRepo (nockInstance, repo) {
@@ -89,10 +89,36 @@ function nockRepo (nockInstance, repo) {
     .reply(201, {
       html_url: 'https://github.com/pkgjs/wiby/pull/1'
     })
-    .get('/repos/wiby-test/pass/branches/running-unit-tests')
+    .get(`/repos/wiby-test/${repo}/branches/running-unit-tests`)
     .reply(200, {
-      name: 'running-unit-tests'
+      name: 'running-unit-tests',
+      commit: {
+        sha: 'head_sha',
+        commit: {
+          tree: {
+            sha: 'tree_sha'
+          }
+        }
+      }
+    })
+    .get(`/repos/wiby-test/${repo}/branches/wiby-running-unit-tests`)
+    .reply(404)
+    .get(`/repos/wiby-test/${repo}/branches/existing-branch`)
+    .reply(404)
+    .get(`/repos/wiby-test/${repo}/branches/wiby-existing-branch`)
+    .reply(200, {
+      name: 'wiby-existing-branch',
+      commit: {
+        sha: 'head_sha',
+        commit: {
+          tree: {
+            sha: 'tree_sha'
+          }
+        }
+      }
     })
+    .patch(`/repos/wiby-test/${repo}/git/refs/heads%2Fwiby-existing-branch`, { sha: 'fake_sha' })
+    .reply(204)
 }
 
 function buildNock () {
diff --git a/test/internals/github-integration.js b/test/internals/github-integration.js
index 336b41c..154377e 100644
--- a/test/internals/github-integration.js
+++ b/test/internals/github-integration.js
@@ -11,7 +11,7 @@ tap.test('package.json can be fetched with a valid url', async tap => {
 }, { skip: !process.env.GITHUB_TOKEN })
 
 tap.test('Shas returned from getShas', async tap => {
-  const [headSha, treeSha] = await github.getShas('pkgjs', 'wiby')
+  const { headSha, treeSha } = await github.getShas('pkgjs', 'wiby')
   tap.notEqual(headSha, null)
   tap.notEqual(treeSha, null)
 }, { skip: !process.env.GITHUB_TOKEN })