---
title: "Test sign-up emails in an Android app (Kotlin) · Proxy Mail QA"
description: "Test email codes, magic links and App Links in a Kotlin Android app: by hand on the emulator with adb, in Espresso or Compose tests, and when links open Chrome."
url: https://proxymail.qa/mobile/android-sign-up-testing
---

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2. [Mobile apps](https://proxymail.qa/mobile)

# Testing sign-up emails in an Android app (Kotlin)

Signing a real Gmail account into every emulator is slow, and one shared inbox soon fills with codes from every run. Use a fresh address per test instead, read the code or link from it, and open the link in your app with one adb command.

Updated October 18, 2026

## Why sign-up emails are awkward to test on Android

- **The emulator’s inbox is the wrong place to look.** Signing in to Gmail on every emulator image takes time, and a shared account mixes codes from every tester and every run.
- **Links have to open the app.** A verify or magic link is usually an `https` App Link. If verification fails, Android 12 and later open it in Chrome without asking, and the flow quietly finishes in the browser.
- **Local links point somewhere else.** On the emulator, `localhost` is the emulator, not your computer.
- **Single-use links break if anything opens them first.** Proxy Mail QA never opens or prefetches a link, so it still works when your test opens it.

## Test it by hand on the emulator

1. **Create an address** in Proxy Mail QA, with a persona and a generated password if your form needs them.
2. **Sign up in the emulator** with it. The emulator shares your computer’s clipboard, so copy and paste works both ways.
3. **Get the code** from the address’s row with **Copy**, and paste it into the app.
4. **Or open the link in the app:** `adb shell "am start -W -a android.intent.action.VIEW -d '<link>'"`. For a `myapp://` link the inbox shows this command next to it, ready to copy.
5. **If Chrome opens instead,** check verification with `adb shell pm get-app-links com.example.app` and retry it with `adb shell pm verify-app-links --re-verify com.example.app`.

## Automate it with Espresso

Add the Kotlin helper from the [Espresso guide](https://proxymail.qa/docs/espresso) to `androidTest`, pass the API key as an instrumentation argument, and the test reads the code itself:

Kotlin

```kotlin
val qa = ProxyMailQA()
val account = qa.createAddress()

onView(withHint("Email")).perform(typeText(account.address), closeSoftKeyboard())
val submitted = Instant.now()
onView(withText("Sign up")).perform(click())

val code = qa.waitForCode(account.address, submitted)
onView(withHint("Code")).perform(typeText(code))

```

In a Compose test, use `composeTestRule.onNodeWithText("Email").performTextInput(account.address)` and so on. To open a link, start an `ACTION_VIEW` intent with it (the [guide](https://proxymail.qa/docs/espresso) has the two lines). If the email has both a web link and a `myapp://` one, `waitForLink(…, app = true)` returns the app’s.

The same helper checks the email itself (`checkEmail` with your App Link domain, and `countEmails` for duplicates), signs in as a saved test account, and adds each test to the pull request’s report: see the [Espresso guide](https://proxymail.qa/docs/espresso#check-the-email-not-just-the-code).

## What to check in your Kotlin code

- **The email field is an email field.** `android:inputType="textEmailAddress"` for views, or `KeyboardOptions(keyboardType = KeyboardType.Email)` in Compose, so the keyboard doesn’t capitalise or “correct” the address.
- **App Links are verified for every build you test.** The intent filter needs `android:autoVerify="true"`, and `https://your-domain/.well-known/assetlinks.json` must list the SHA-256 fingerprint of the certificate that signed the build: your debug key for local builds, Google’s app signing key for builds from Google Play.
- **The link works from a cold start and a warm one.** A link that launches the app arrives in `onCreate` as `intent.data`. If the activity is already running with `singleTop` or `singleTask`, it arrives in `onNewIntent` instead, and is easy to miss. With Navigation Compose, a `navDeepLink` on the destination handles both.
- **The link is still single-use.** Open it twice: the second time should explain that it was used.
- **Links don’t point at your computer.** Use your staging address in the emails, not `localhost` or `10.0.2.2`. See [links that point at localhost](https://proxymail.qa/solve/localhost-links).

Using Firebase email-link sign-in? Its App Links use your Firebase Hosting domain: see [Firebase email-link sign-in on mobile](https://proxymail.qa/mobile/firebase-email-link).

## Try it on your next sign-up test

Free plan, no credit card. Create an address and watch the code or link arrive.

[Create a free account](https://app.proxymail.qa/?mode=signup)

## Questions

### Why does my verification link open in Chrome instead of my app?

From Android 12, an https link opens in your app only when its App Links are verified for that domain; otherwise it opens in the browser. Run adb shell pm get-app-links with your package name to see the state. The usual causes are a missing assetlinks.json, or one listing the wrong signing certificate: the debug key for a debug build, or Google's app signing key (not your upload key) for a build from Google Play.

### Why can't the emulator open a link to localhost?

On the Android emulator, localhost is the emulator itself. It reaches your computer at 10.0.2.2\. Proxy Mail QA flags links to localhost and to 10.0.2.2 so you can tell a local link from a broken one: see proxymail.qa/solve/localhost-links.

### Does this work with Jetpack Compose?

Yes. The helper doesn't care how the screen is built: type the address with Espresso's typeText for views, or performTextInput in a Compose test.

### Can I test codes sent by text message?

No. Proxy Mail QA receives email only. Codes sent by SMS need a different tool.

## Related guides

- [Test sign-up emails in a SwiftUI or UIKit appCodes and Universal Links in the iOS simulator, by hand or in XCUITest, and the cold-start link bug to check for.](https://proxymail.qa/mobile/ios-sign-up-testing)
- [Test sign-up emails and magic links in React Native and Expoexp:// and myapp:// links from Expo Go and development builds, opened in the simulator or from Detox.](https://proxymail.qa/mobile/react-native-expo)
- [Test sign-up emails in a Flutter appCodes in integration tests, deep links on both platforms, and Supabase or Firebase redirects that open the app.](https://proxymail.qa/mobile/flutter)
- [Test Firebase email-link sign-in on iOS and AndroidThe setup after Dynamic Links shut down, and how to test the link opening the app on the same and another device.](https://proxymail.qa/mobile/firebase-email-link)

[See every email testing problem we solve](https://proxymail.qa/solve)