How to use Arb.trampoline method of io.kotest.property.arbitrary.map class

1package com.example.sdk.usecases2import com.example.sdk.*3import com.example.sdk.api.PokemonAPI4import com.example.sdk.api.ShakespeareAPI5import com.example.sdk.api.requests.ShakespeareTranslateRequest6import com.example.sdk.api.responses.PokemonSpeciesResponse7import com.example.sdk.api.responses.PokemonSpeciesResponse.FlavorObject8import com.example.sdk.api.responses.PokemonSpeciesResponse.Language9import com.example.sdk.api.responses.ShakespeareTranslateResponse10import com.example.sdk.api.responses.ShakespeareTranslateResponse.Contents11import io.kotest.assertions.fail12import io.kotest.core.spec.style.FunSpec13import io.kotest.matchers.collections.shouldBeEmpty14import io.kotest.property.Arb15import io.kotest.property.arbitrary.of16import io.kotest.property.forAll17import io.reactivex.rxjava3.core.Single18import io.reactivex.rxjava3.observers.TestObserver19import io.reactivex.rxjava3.schedulers.Schedulers20import org.mockito.kotlin.any21import org.mockito.kotlin.argThat22import org.mockito.kotlin.mock23import org.mockito.kotlin.whenever24import retrofit2.HttpException25import java.net.SocketTimeoutException26class RetrieveShakespeareDescriptionUseCaseTest : FunSpec({27    val validSpeciesResponse = listOf(28        PokemonSpeciesResponse(listOf(FlavorObject("first", Language("en")))),29        PokemonSpeciesResponse(30            listOf(31                FlavorObject("secondo", Language("it")),32                FlavorObject("zweite", Language("de")),33                FlavorObject("second", Language("en"))34            )35        ),36        PokemonSpeciesResponse(37            listOf(38                FlavorObject("third", Language("en")),39                FlavorObject("terzo", Language("it"))40            )41        )42    )43    val invalidSpeciesResponse = listOf(44        PokemonSpeciesResponse(listOf()),45        PokemonSpeciesResponse(46            listOf(47                FlavorObject("quarto", Language("it")),48                FlavorObject("vierte", Language("de"))49            )50        )51    )52    val possibleShakespeareRequests = listOf(53        ShakespeareTranslateRequest("first"),54        ShakespeareTranslateRequest("second"),55        ShakespeareTranslateRequest("third")56    )57    val shakespeareApiResponse = ShakespeareTranslateResponse(Contents("success"))58    // Errors59    val pokemonApiError = IllegalArgumentException("Pokemon API error")60    val shakespeareApiError = IllegalArgumentException("Shakespeare API error")61    // Generators62    val speciesResponseGenerator = Arb.of(validSpeciesResponse + invalidSpeciesResponse)63    val shakespeareResponseGenerator = Arb.of(64        listOf(65            Single.just(shakespeareApiResponse),66            Single.error(shakespeareApiError)67        )68    )69    test("RetrieveShakespeareDescriptionUseCase Property-Based test") {70        forAll(71            pokemonNameGenerator,72            speciesResponseGenerator,73            shakespeareResponseGenerator74        ) { pokemonName, speciesResponse, shakespeareResponse ->75            // Mocks76            val pokemonClient: PokemonAPI = mock()77            whenever(pokemonClient.getPokemonSpecies(argThat {78                validPokemonList.map { it.lowercase() }.contains(this.lowercase())79            }))80                .thenReturn(Single.just(speciesResponse))81            whenever(pokemonClient.getPokemonSpecies(argThat {82                invalidPokemonList.map { it.lowercase() }.contains(this.lowercase())83            }))84                .thenReturn(Single.error(pokemonApiError))85            val shakespeareClient: ShakespeareAPI = mock()86            whenever(shakespeareClient.getShakespeareText(argThat {87                possibleShakespeareRequests.contains(this)88            }))89                .thenReturn(shakespeareResponse)90            // Observer-test91            val testObserver = TestObserver.create<String>()92            // Test execution93            RetrieveShakespeareDescriptionUseCase(94                pokemonClient,95                shakespeareClient,96                Schedulers.trampoline()97            )98                .execute(pokemonName)99                .subscribe(testObserver)100            // Checks101            when {102                testObserver.values().isEmpty() -> testObserver.assertError {103                    when (it) {104                        is SdkError.Generic -> {105                            invalidPokemonList.contains(pokemonName) ||106                                    shakespeareResponse.test().values().isEmpty()107                        }108                        is SdkError.NoEnglishDescriptionFound ->109                            invalidSpeciesResponse.contains(speciesResponse)110                        else -> fail("Unexpected error, $it")111                    }112                }113                testObserver.values().isNotEmpty() -> testObserver.assertValueCount(1)114                    .assertValue {115                        shakespeareResponse.blockingGet() == shakespeareApiResponse &&116                                it == "success"117                    }118                else -> fail("Unexpected result, ${testObserver.values()}")119            }120            true121        }122    }123    test("RetrieveShakespeareDescriptionUseCase pokemon api ERROR test") {124        forAll(createApiExceptionGenerator<PokemonSpeciesResponse>()) { exception ->125            val client: PokemonAPI = mock()126            whenever(client.getPokemonSpecies(any()))127                .thenReturn(Single.error(exception))128            val shakespeareClient: ShakespeareAPI = mock()129            whenever(shakespeareClient.getShakespeareText(any()))130                .thenReturn(Single.just(shakespeareApiResponse))131            val testObserver = TestObserver.create<String>()132            RetrieveShakespeareDescriptionUseCase(133                client,134                shakespeareClient,135                Schedulers.trampoline()136            )137                .execute("")138                .subscribe(testObserver)139            testObserver.values().shouldBeEmpty()140            testObserver.assertError { errorAssert(it, exception) }141            true142        }143    }144    test("RetrieveShakespeareDescriptionUseCase shakespeare api ERROR test") {145        forAll(createApiExceptionGenerator<ShakespeareTranslateResponse>()) { exception ->146            val client: PokemonAPI = mock()147            whenever(client.getPokemonSpecies(any()))148                .thenReturn(149                    Single.just(150                        PokemonSpeciesResponse(listOf(FlavorObject("first", Language("en"))))151                    )152                )153            val shakespeareClient: ShakespeareAPI = mock()154            whenever(shakespeareClient.getShakespeareText(any()))155                .thenReturn(Single.error(exception))156            val testObserver = TestObserver.create<String>()157            RetrieveShakespeareDescriptionUseCase(158                client,159                shakespeareClient,160                Schedulers.trampoline()161            )162                .execute("")163                .subscribe(testObserver)164            testObserver.values().shouldBeEmpty()165            testObserver.assertError { errorAssert(it, exception) }166            true167        }168    }169})170private fun errorAssert(it: Throwable, exception: Exception) = when (it) {171    is SdkError.Http -> {172        when (it._message) {173            "Too many request done" -> (exception as HttpException).code() == 429174            "Internal server error" -> (exception as HttpException).code() == 500175            "Resource not found" -> (exception as HttpException).code() == 404176            else -> fail("Unexpected exception, $it")177        }178    }179    is SdkError.Generic -> exception is NullPointerException180    SdkError.TimeOut -> exception is SocketTimeoutException181    else -> fail("Unexpected exception, $it")182}...

1package com.example.sdk.usecases2import com.example.sdk.*3import com.example.sdk.api.PokemonAPI4import com.example.sdk.api.responses.PokemonDetailResponse5import com.example.sdk.api.responses.PokemonDetailResponse.Sprites6import io.kotest.assertions.fail7import io.kotest.core.spec.style.FunSpec8import io.kotest.property.Arb9import io.kotest.property.arbitrary.of10import io.kotest.property.forAll11import io.reactivex.rxjava3.core.Single12import io.reactivex.rxjava3.observers.TestObserver13import io.reactivex.rxjava3.schedulers.Schedulers14import org.mockito.kotlin.any15import org.mockito.kotlin.argThat16import org.mockito.kotlin.mock17import org.mockito.kotlin.whenever18import retrofit2.HttpException19import java.net.SocketTimeoutException20import java.net.URL21class RetrievePokemonSpriteUseCaseTest : FunSpec({22    val validResponse = listOf(23        PokemonDetailResponse(Sprites("https://mysite.com", "w.site.c")),24        PokemonDetailResponse(Sprites("https://mysite.com", null)),25        PokemonDetailResponse(Sprites(null, "https://www.google.it")),26        PokemonDetailResponse(Sprites("www.malformed.c", "https://www.google.it")),27        PokemonDetailResponse(Sprites("https://mysite.com", "https://www.google.it"))28    )29    val invalidUrlResponse = listOf(30        PokemonDetailResponse(Sprites(null, null)),31        PokemonDetailResponse(Sprites(null, "ww.invalid-url.com")),32        PokemonDetailResponse(Sprites("htp:wwww-yr", "ww.invalid-url.com")),33        PokemonDetailResponse(Sprites("htp:wwww-yr", null))34    )35    // Generators36    val responseGenerator = Arb.of(validResponse + invalidUrlResponse)37    // Errors38    val apiError = IllegalArgumentException("API error")39    test("RetrievePokemonSpriteUseCase Property-Based test") {40        forAll(pokemonNameGenerator, responseGenerator) { pokemonName, response ->41            // Mocks42            val client: PokemonAPI = mock()43            whenever(client.getPokemonDetail(argThat {44                validPokemonList.map { it.lowercase() }.contains(this.lowercase())45            }))46                .thenReturn(Single.just(response))47            whenever(client.getPokemonDetail(argThat {48                invalidPokemonList.map { it.lowercase() }.contains(this.lowercase())49            }))50                .thenReturn(Single.error(apiError))51            // Observer-test52            val testObserver = TestObserver.create<URL>()53            // Test execution54            RetrievePokemonSpriteUseCase(55                client,56                Schedulers.trampoline(),57                Dependencies.urlValidator58            )59                .execute(pokemonName)60                .subscribe(testObserver)61            // Checks62            when {63                testObserver.values().isEmpty() -> testObserver.assertError {64                    when (it) {65                        is SdkError.Generic -> invalidPokemonList.contains(pokemonName)66                        is SdkError.NoValidPokemonSpriteFound ->67                            invalidUrlResponse.contains(response)68                        else -> fail("Unexpected error, $it")69                    }70                }71                testObserver.values().isNotEmpty() -> testObserver.assertValueCount(1)72                    .assertValue {73                        when (it) {74                            URL("https://mysite.com") ->75                                response.sprites.frontDefault == "https://mysite.com"76                            URL("https://www.google.it") ->77                                response.sprites.frontDefault == null ||78                                        response.sprites.frontDefault == "www.malformed.c"79                            else -> fail("Unexpected URL, $it")80                        }81                    }82                else -> fail("Unexpected result, ${testObserver.values()}")83            }84            true85        }86    }87    test("RetrievePokemonSpriteUseCase ERROR test") {88        forAll(createApiExceptionGenerator<PokemonDetailResponse>()) { exception ->89            val client: PokemonAPI = mock()90            whenever(client.getPokemonDetail(any()))91                .thenReturn(Single.error(exception))92            val testObserver = TestObserver.create<URL>()93            RetrievePokemonSpriteUseCase(94                client,95                Schedulers.trampoline(),96                Dependencies.urlValidator97            )98                .execute("")99                .subscribe(testObserver)100            testObserver.assertError {101                when (it) {102                    is SdkError.Http -> {103                        when (it._message) {104                            "Too many request done" -> (exception as HttpException).code() == 429105                            "Internal server error" -> (exception as HttpException).code() == 500106                            "Resource not found" -> (exception as HttpException).code() == 404107                            else -> fail("Unexpected exception, $it")108                        }109                    }110                    is SdkError.Generic -> exception is NullPointerException111                    SdkError.TimeOut -> exception is SocketTimeoutException112                    else -> fail("Unexpected exception, $it")113                }114            }115            true116        }117    }118})...

1package io.kotest.property.arbitrary2import io.kotest.property.Arb3import io.kotest.property.RandomSource4import io.kotest.property.Sample5import io.kotest.property.map6/**7 * Returns a new [Arb] which takes its elements from the receiver and maps them using the supplied function.8 */9fun <A, B> Arb<A>.map(fn: (A) -> B): Arb<B> = trampoline { sampleA ->10   object : Arb<B>() {11      override fun edgecase(rs: RandomSource): B? = fn(sampleA.value)12      override fun sample(rs: RandomSource): Sample<B> {13         val value = fn(sampleA.value)14         val shrinks = sampleA.shrinks.map(fn)15         return Sample(value, shrinks)16      }17   }18}19/**20 * Returns a new [Arb] which takes its elements from the receiver and maps them using the supplied function.21 */22fun <A, B> Arb<A>.flatMap(fn: (A) -> Arb<B>): Arb<B> = trampoline { fn(it.value) }23/**24 * Returns a new [TrampolineArb] from the receiver [Arb] which composes the operations of [next] lambda25 * using a trampoline method. This allows [next] function to be executed without exhausting call stack.26 */27internal fun <A, B> Arb<A>.trampoline(next: (Sample<A>) -> Arb<B>): Arb<B> = when (this) {28   is TrampolineArb -> this.thunk(next)29   else -> TrampolineArb(this).thunk(next)30}31/**32 * The [TrampolineArb] is a special Arb that exchanges call stack with heap.33 * In a nutshell, this arb stores command chains to be applied to the original arb inside a list.34 * This technique is an imperative reduction of Free Monads. This eliminates the need of creating intermediate35 * Trampoline Monad and tail-recursive function on those which can be expensive.36 * This minimizes the amount of code and unnecessary object allocation during sample generation in the expense of typesafety.37 *38 * This is an internal implementation. Do not use this TrampolineArb as is and please do not expose this39 * to users outside of the library. For library maintainers, please use the [Arb.trampoline] extension function.40 * The extension function will provide some type-guardrails to workaround the loss of types within this Arb.41 */42@Suppress("UNCHECKED_CAST")43internal class TrampolineArb<A> private constructor(44   private val first: Arb<A>,45   private val commands: List<(Sample<Any>) -> Arb<Any>>46) : Arb<A>() {47   constructor(first: Arb<A>) : this(first, emptyList())48   fun <A, B> thunk(fn: (Sample<A>) -> Arb<B>): TrampolineArb<B> =49      TrampolineArb(50         first,51         commands + (fn as (Sample<Any>) -> Arb<Any>)52      ) as TrampolineArb<B>53   override fun edgecase(rs: RandomSource): A? =54      commands55         .fold(first as Arb<Any>) { currentArb, next ->56            val currentEdge = currentArb.edgecase(rs) ?: currentArb.sample(rs).value57            next(Sample(currentEdge))58         }59         .edgecase(rs) as A?60   override fun sample(rs: RandomSource): Sample<A> =61      commands62         .fold(first as Arb<Any>) { currentArb, next ->63            next(currentArb.sample(rs))64         }65         .sample(rs) as Sample<A>66}...

1package io.kotest.property.arbitrary2import io.kotest.property.Arb3import io.kotest.property.PropertyTesting4import io.kotest.property.RTree5import io.kotest.property.RandomSource6import io.kotest.property.Sample7import io.kotest.property.filter8/**9 * Returns a new [Arb] which takes its elements from the receiver and filters them using the supplied10 * predicate. This gen will continue to request elements from the underlying gen until one satisfies11 * the predicate.12 */13fun <A> Arb<A>.filter(predicate: (A) -> Boolean): Arb<A> = trampoline { sampleA ->14   object : Arb<A>() {15      override fun edgecase(rs: RandomSource): A? =16         sequenceOf(sampleA.value)17            .plus(generateSequence { this@filter.edgecase(rs) })18            .take(PropertyTesting.maxFilterAttempts)19            .filter(predicate)20            .firstOrNull()21      override fun sample(rs: RandomSource): Sample<A> {22         val sample = sequenceOf(sampleA).plus(this@filter.samples(rs)).filter { predicate(it.value) }.first()23         return Sample(sample.value, sample.shrinks.filter(predicate) ?: RTree({ sample.value }))24      }25   }26}27/**28 * @return a new [Arb] by filtering this arbs output by the negated function [f]29 */30fun <A> Arb<A>.filterNot(f: (A) -> Boolean): Arb<A> = filter { !f(it) }31/**32 * Create a new [Arb] by keeping only instances of B generated by this gen.33 * This is useful if you have a type hierarchy and only want to retain34 * a particular subtype.35 */36@Suppress("UNCHECKED_CAST")37inline fun <A, reified B : A> Arb<A>.filterIsInstance(): Arb<B> = filter { it is B }.map { it as B }...

1val arb = Arb . trampoline ( Arb . int ( ) )2val arb = Arb . trampoline ( Arb . int ( ) )3val arb = Arb . trampoline ( Arb . int ( ) )4val arb = Arb . trampoline ( Arb . int ( ) )5val arb = Arb . trampoline ( Arb . int ( ) )6val arb = Arb . trampoline ( Arb . int ( ) )7val arb = Arb . trampoline ( Arb . int ( ) )

1val arbB = Arb.trampoline { arbA.map { a -> listOf(a) } }2arbB.generate(rs).take(100).forEach { println(it) }3val arbB = Arb.trampoline { arbA.map { a -> listOf(a) } }4arbB.generate(rs).take(100).forEach { println(it) }5val arbB = Arb.trampoline { arbA.map { a -> listOf(a) } }6arbB.generate(rs).take(100).forEach { println(it) }7val arbB = Arb.trampoline { arbA.map { a -> listOf(a) } }8arbB.generate(rs).take(100).forEach { println(it) }9val arbB = Arb.trampoline { arbA.map { a -> listOf(a) } }10arbB.generate(rs).take(100).forEach { println(it) }