Testing

Dependency

To simplify testing your Formulas, use formula-test module.

testImplementation 'com.instacart.formula:formula-test:{latest_version}'

Basic example

Use test extension to start testing your formula. Then, you can use output function to make assertions on the output or invoke event listeners.

CounterFormula()
    .test()
    // Making assertion on the initial output
    .output {
        assertThat(count).isEqualTo("Count: 0")
    }
    // Invoking an event listener that live on the output.
    .output { onIncrement() }
    .output { onIncrement() }
    // Making assertion on final output
    .output {
       assertThat(count).isEqualTo("Count: 2")
    }

Note: you can find the CounterFormula in the samples folder in the repository.

Fakes and Mocks

In some tests, we want to provide a fake/mock implementation of formula that can emit an output, check data passed by the parent or pass events back to the parent.

Mockito example

val testFormula = TestFormula<MyFormula.Input, MyFormula.Output>(
    initialOutput = MyFormula.Output()
)
// We only want to override the `implementation()` function and keep default `type()`.
val formula = mock<MyFormula>(defaultAnswer = CallsRealMethods())
whenever(formula.implementation()).thenReturn(testFormula)

Using interfaces and fakes in your testing

interface MyFormula : IFormula<MyFormula.Input, MyFormula.Output> {
    class MyInput()
    class MyOutput()
}

// Test fake implementation
class FakeMyFormula : MyFormula {
  val testFormula = TestFormula<MyFormula.Input, MyFormula.Output>(
      initialOutput = MyFormula.Output()
  )

  override fun implementation() = testFormula
}

Interacting with Test Formula

val testFormula = TestFormula()

// Assert on the data passed
testFormula.input {  
    assertThat(this.id).isEqualTo(1)
}

// Trigger an event 
testFormula.input {
    this.onTextChanged("new text")
}

// Emit a new output
testFormula.output(MyFormula.Output())