Why Your OTP & Email Tests Fail in CI (And How I Finally Fixed It)

🧠 The Problem No One Talks About

If you’ve ever tested a signup flow with email verification or OTP… you’ve probably seen this:

• Tests pass locally ✅

• CI randomly fails ❌

• Retries create weird edge cases 🤯

And the worst part?

👉 You don’t know why it failed.

Was it:

• Email delay?

• Wrong OTP picked?

• Parsing issue?

• Multiple emails sent?

Most tools don’t tell you. They just give you:

“Timeout exceeded”

⚠️ The Real Issue: Email Is an Async System

Most developers treat email in tests like a simple API response.

But it’s not.

It’s a distributed, asynchronous system:

• Email provider latency varies (1–5s+)

• Retries can generate multiple emails

• OTP parsing can fail silently

• CI environments behave differently than local

This is why:

👉 Mocking works… until it doesn’t
👉 Real email testing works… but becomes flaky

🧪 What I Tried (And Why It Didn’t Work)

1. Mocking Email

• Fast ✅

• Deterministic ✅

• Completely unrealistic ❌

👉 Doesn’t catch real delivery issues

2. Using Temp Mail Tools

• Easy to use ✅

• Works for basic flows ✅

But tools like typical temp mail platforms are built for:

• privacy

• spam avoidance

not for:

👉 testing auth systems

3. Polling APIs (Mailosaur, etc.)

• Better than scraping ✅

• Still limited ❌

Problem:

👉 You still don’t know what happened inside the flow

💡 The Breakthrough: Track the Full Flow

Instead of just waiting for OTP…

I started tracking:

• when the email was triggered

• when it actually arrived

• when OTP was extracted

• how long each step took

Example:

Signup triggered → 0ms 
Email received → 3.8s 
OTP extracted → 4.1s 

Suddenly:

👉 failures weren’t random anymore
👉 they were explainable

🔥 This Changed Everything

Now instead of:

❌ “Test failed”

I get:

Email delayed by 4.2s → exceeded timeout

And that’s a completely different experience.

🧰 What I Built Around This

I ended up building a small system around this idea:

• programmatic inbox creation

• real-time email detection

• OTP extraction

• timeline debugging

• CI-friendly APIs + SDKs

So instead of just:

await waitForOtp()

You actually understand:

👉 what happened behind the scenes

If you’re curious, this is what I’ve been working on:
https://www.freecustom.email/api

🤔 Question for You

How are you currently testing email/OTP flows?

• Fully mocked?

• Using temp mail tools?

• Real provider testing in CI?

And more importantly:

👉 how do you debug failures when they happen?

💬 Final Thought

Most developers don’t struggle with writing tests.

They struggle with:

👉 understanding why tests fail

And email-based auth flows are one of the biggest hidden sources of that pain.