How do people tend to unit test DSL functions like...

# getting-started

[Scott Whitman]

How do people tend to unit test DSL functions like the address function below? What are some good practices to handle the Address.Builder dependency?

fun main() {
    val address = address {
        street = "123 Any St."
        city = "Any city"
    }
    
    println(address)
}

fun address(lambda: Address.Builder.() -> Unit): Address {
    return Address.Builder().apply(lambda).build()
}

data class Address(
    val street: String,
    val city: String
) {
    class Builder {
        var street: String? = null
        var city: String? = null
        
        fun build(): Address {
            return Address(street!!, city!!)
        }
    }
}

[jbnizet]

Use the DSL in your tests just like a real user of the DSL would, and check it does what it’s expected to do:

class AddressDslTest {
    @Test
    fun `should allow creating an address`() {
        val result = address {
            street = "Downing street"
            city = "London"
        }

        assertEquals(Address("Downing street", "London"), result)
    }
}

[jbnizet]

Adding a test where you forget to set the street or the city should give you ideas about how you could improve the code.

[Scott Whitman]

How about when the DSL is nested? Another example, to unit test this person DSL function, It seems I would need to have home and address in my person unit tests.

person {
    home {
        address {
            ...
        }
        ...
    }
    ...
}

[jbnizet]

I don’t se any reason not to apply the same principle.

[Matteo Mirk]

it’s the same: just check the built object has the expected values, and you’ll test the builder indirectly