parameterized-tests

name	parameterized-tests
description	Use when writing, converting, or reviewing parameterized JVM, Robolectric, instrumentation, or Paparazzi tests in stripe-android. Covers TestParameterInjector runners, source-set dependencies, method versus class parameters, value providers, case matrices, and stable test names.

Parameterized Tests

Use TestParameterInjector to give each case an independent test result while keeping repeated behavior in one test method.

Select the runner and dependency

Declare TestParameterInjector directly in the module and source set that compiles the test:

testImplementation testLibs.testParameterInjector
androidTestImplementation testLibs.testParameterInjector

Use only the declaration needed by that source set. Do not rely on another module or source set to provide it transitively.

Test type	Runner
JVM, instrumentation, or Paparazzi	TestParameterInjector
Robolectric JVM	RobolectricTestParameterInjector

@RunWith(TestParameterInjector::class)
internal class FeeCalculatorTest

@RunWith(RobolectricTestParameterInjector::class)
internal class FeeCalculatorRobolectricTest

Import RobolectricTestParameterInjector from org.robolectric. Import the other runner and annotations from com.google.testing.junit.testparameterinjector.

Put focused cases on the test method

Parameterize the method when the cases apply to one test. This keeps unrelated tests from running across the same matrix.

@Test
fun `calculates the expected fee`(
    @TestParameter(valuesProvider = FeeCaseProvider::class)
    testCase: FeeCase,
) {
    assertThat(calculateFee(testCase.input)).isEqualTo(testCase.expected)
}

Use a class field or constructor parameter only when every test in the class intentionally shares that parameter matrix.

Choose the smallest value source

Use enum and boolean shorthand when every value is meaningful:

@Test
fun `updates state`(
    @TestParameter mode: Mode,
    @TestParameter enabled: Boolean,
) {
    // Runs the Cartesian product of every mode and boolean value.
}

Use one curated case object when only specific combinations are valid or when inputs and expected outputs belong together. Multiple @TestParameter arguments produce a Cartesian product.

Use the modern TestParameterValuesProvider, not the deprecated nested provider interface:

internal object FeeCaseProvider : TestParameterValuesProvider() {
    override fun provideValues(
        context: TestParameterValuesProvider.Context?,
    ): List<FeeCase> = listOf(
        FeeCase(name = "Standard", input = 100, expected = 3),
        FeeCase(name = "Expedited", input = 100, expected = 8),
    )
}

internal data class FeeCase(
    val name: String,
    val input: Int,
    val expected: Int,
) {
    override fun toString(): String = name
}

Give curated cases stable, readable names. Override toString() when the framework should derive test identifiers from the case.

Check the result

1. Run the focused parameterized test class and confirm the expected case count and names.
2. Run the module's required static and API checks.
3. Run git diff --check.