---
name: create-fake
description: Explains how to create a fake following stripe-android's coding standards
---
# Creating Fakes for Testing
This skill describes how to create fake implementations for testing in the Stripe Android SDK. The codebase **strongly prefers fakes over mocks** for better test reliability and clarity.
## Core Principles
1. **Prefer fakes over mocks** - Create `FakeClassName` implementations that provide controllable, inspectable behavior
2. **Use Turbine for call tracking** - Track method invocations with Turbine channels for verification
3. **Provide default parameters** - Make fakes easy to instantiate with sensible defaults
4. **Enable validation** - Implement `ensureAllEventsConsumed()` validation method when using Turbines
## Basic Fake Structure
### File Naming and Location
- Place fakes in the test source directory: `src/test/java/com/stripe/android/.../FakeClassName.kt`
- Name pattern: `Fake` + interface/class name (e.g., `FakeEventReporter`, `FakeCustomerRepository`)
- Mark as `internal` to scope to the test module
### Constructor Pattern
Always use **default parameters** to make instantiation easy:
```kotlin
internal class FakeCustomerRepository(
private val paymentMethods: List<PaymentMethod> = emptyList(),
private val customer: Customer? = null
) : CustomerRepository {
// Implementation
}
```
For complex setup, provide a **companion object factory method**:
```kotlin
internal class FakePaymentMethodVerticalLayoutInteractor(
initialState: PaymentMethodVerticalLayoutInteractor.State,
initialShowsWalletsHeader: Boolean = false,
private val viewActionRecorder: ViewActionRecorder<PaymentMethodVerticalLayoutInteractor.ViewAction>
) : PaymentMethodVerticalLayoutInteractor {
companion object {
fun create(
paymentMethodMetadata: PaymentMethodMetadata = PaymentMethodMetadataFactory.create(),
initialShowsWalletsHeader: Boolean = true,
viewActionRecorder: ViewActionRecorder<PaymentMethodVerticalLayoutInteractor.ViewAction> = ViewActionRecorder()
): FakePaymentMethodVerticalLayoutInteractor {
// Complex initialization logic
val initialState = /* construct complex state */
return FakePaymentMethodVerticalLayoutInteractor(
initialState = initialState,
initialShowsWalletsHeader = initialShowsWalletsHeader,
viewActionRecorder = viewActionRecorder
)
}
}
}
```
## Tracking Method Calls with Turbine
### Basic Turbine Pattern
Directly expose Turbines for test verification:
```kotlin
internal class FakeEventReporter : EventReporter {
val paymentFailureCalls = Turbine<PaymentFailureCall>()
val paymentSuccessCalls = Turbine<PaymentSuccessCall>()
override fun onPaymentFailure(error: Throwable, source: PaymentEventSource) {
paymentFailureCalls.add(PaymentFailureCall(error, source))
}
override fun onPaymentSuccess(paymentMethod: PaymentMethod) {
paymentSuccessCalls.add(PaymentSuccessCall(paymentMethod))
}
}
```
### Data Classes for Call Capture
Define **data classes** to capture method call parameters:
```kotlin
data class PaymentFailureCall(val error: Throwable, val source: PaymentEventSource)
data class PaymentSuccessCall(val paymentMethod: PaymentMethod)
data class DetachRequest(val paymentMethodId: String, val customerId: String)
```
### Validation with ensureAllEventsConsumed
Implement a **validation method** that ensures all turbine events were consumed:
```kotlin
fun ensureAllEventsConsumed() {
paymentFailureCalls.ensureAllEventsConsumed()
paymentSuccessCalls.ensureAllEventsConsumed()
detachRequests.ensureAllEventsConsumed()
updateRequests.ensureAllEventsConsumed()
// ... validate all turbines
}
```
Tests should call this method after verification:
```kotlin
@Test
fun `test payment flow`() = runTest {
val fake = FakeEventReporter()
// Perform operations
fake.onPaymentSuccess(paymentMethod)
// Verify calls
assertThat(fake.paymentSuccessCalls.awaitItem()).isEqualTo(
PaymentSuccessCall(paymentMethod)
)
// Validate all events consumed
fake.ensureAllEventsConsumed()
}
```
## ViewActionRecorder Pattern
For classes that handle view actions, use **ViewActionRecorder**:
```kotlin
internal class FakePaymentMethodVerticalLayoutInteractor(
initialState: PaymentMethodVerticalLayoutInteractor.State,
private val viewActionRecorder: ViewActionRecorder<PaymentMethodVerticalLayoutInteractor.ViewAction>
) : PaymentMethodVerticalLayoutInteractor {
override fun handleViewAction(viewAction: PaymentMethodVerticalLayoutInteractor.ViewAction) {
viewActionRecorder.record(viewAction)
// Optional: implement state changes based on action
}
}
```
**Include ViewActionRecorder in factory with default**:
```kotlin
companion object {
fun create(
paymentMethodMetadata: PaymentMethodMetadata = PaymentMethodMetadataFactory.create(),
viewActionRecorder: ViewActionRecorder<PaymentMethodVerticalLayoutInteractor.ViewAction> = ViewActionRecorder()
): FakePaymentMethodVerticalLayoutInteractor {
return FakePaymentMethodVerticalLayoutInteractor(
initialState = /* ... */,
viewActionRecorder = viewActionRecorder
)
}
}
```
## Excellent Real-World Examples
Reference these fakes from the codebase as gold standards:
### **FakeEventReporter**
`paymentsheet/src/test/java/com/stripe/android/paymentsheet/analytics/FakeEventReporter.kt`
- 16 different Turbine channels for comprehensive event tracking
- Clean `validate()` method checking all turbines
- Data classes for each event type
- Gold standard for Turbine usage
### **FakeCustomerRepository**
`paymentsheet/src/test/java/com/stripe/android/utils/FakeCustomerRepository.kt`
- Excellent use of default parameters
- Multiple Turbines for tracking different operations (detach, update, setDefault)
- Data classes for request tracking
### **FakePaymentMethodVerticalLayoutInteractor**
`paymentsheet/src/test/java/com/stripe/android/paymentsheet/verticalmode/FakePaymentMethodVerticalLayoutInteractor.kt`
- ViewActionRecorder integration
- Companion object factory method with sophisticated defaults
## Quick Reference
- **Need to track method calls?** → Use Turbine with data classes
- **Tracking view actions?** → Use ViewActionRecorder
- **Need to verify all events consumed?** → Implement `ensureAllEventsConsumed()` that calls it on all Turbines
- **Complex initialization?** → Add companion object `create()` factory method
- **Always** → Provide default parameters for easy instantiation
