Optimus

Stop hardcoding test responses. Switch mock behavior at runtime — without recompiling.

Optimus wraps Retrofit with a declarative mock layer. Define every possible response your API could return, mark one as the default, and flip between them at runtime from a debug UI or in tests. No more rebuilds to reproduce edge cases.

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How it works

1. Declare your mock responses

class MockUser : MockResponse {
    @Default
    val HTTP200 = success { User(id = 1) }
    val HTTP401 = error(401, "Unauthorized") { ApiError(401, "Unauthorized") }
    val HTTP503 = error(503, "Service Unavailable") {}
}

2. Wire it up once

val supplier = MockResponseSupplier.create(sharedPreferences)

val optimus = Optimus.Builder(supplier)
    .retrofit(retrofit, sharedPreferences)
    .mockGraph(
        alter(Api::class.java, "Api") {
            Api::login with MockUser::class named "Login"
        }
    )
    .converter(Converter.create(moshi))
    .build()

3. Use it like a regular Retrofit service

val api = optimus.create(Api::class.java)

4. Switch responses at runtime via the debug UI

AlertDialog.Builder(this)
    .setView(OptimusView(this).apply { setOptimus(optimus) })
    .show()

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Testing

Optimus makes unit and UI tests precise — no network calls, no random failures.

// Set up with an in-memory supplier
val supplier = MockResponseSupplier.memory()
val optimus = Optimus.Builder(supplier).retrofit(retrofit).mockGraph(mockGraph).build()

// Pin the exact response you want to test
mockResponseSupplier.set(Api::login, MockUser::HTTP401)
assertThat(api.login().code()).isEqualTo(401)

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Installation

dependencies {
    implementation("com.cocosw:optimus:2.0.0")
}