How to use Arb.Companion.string method of class

Best Kotest code snippet using


Source:strings.kt Github


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1package kotlin.random.nextInt6/**7 * Returns an [Arb] where each random value is a String of length between minSize and maxSize.8 * By default, the arb uses a [ascii] codepoint generator, but this can be substituted9 * with any codepoint generator. There are many available, such as [katakana] and so on.10 *11 * The edge case values are a string of min length, using the first12 * edge case codepoint provided by the codepoints arb. If the min length is 0 and maxSize > 0, then13 * the edge cases will include a string of length 1 as well.14 */15fun Arb.Companion.string(16 minSize: Int = 0,17 maxSize: Int = 100,18 codepoints: Arb<Codepoint> = Codepoint.ascii()19): Arb<String> {20 return ArbitraryBuilder.create { rs ->21 val size = rs.random.nextInt(minSize..maxSize)22 codepoints.take(size, rs).joinToString("") { it.asString() }23 }.withEdgecaseFn { rs ->24 if (minSize == maxSize) null else {25 val lowCodePoint = codepoints.edgecase(rs)26 val min = lowCodePoint?.let { cp -> List(minSize) { cp.asString() }.joinToString("") }27 val minPlus1 = lowCodePoint?.let { cp -> List(minSize + 1) { cp.asString() }.joinToString("") }28 val edgeCases = listOfNotNull(min, minPlus1)29 .filter { it.length in minSize..maxSize }30 if (edgeCases.isEmpty()) null else edgeCases.random(rs.random)31 }32 }.withShrinker(StringShrinkerWithMin(minSize))33 .withClassifier(StringClassifier(minSize, maxSize))34 .build()35}36/**37 * Returns an [Arb] where each random value is a String which has a length in the given range.38 * By default the arb uses a [ascii] codepoint generator, but this can be substituted39 * with any codepoint generator. There are many available, such as [katakana] and so on.40 *41 * The edge case values are a string of the first value in the range, using the first edge case42 * codepoint provided by the codepoints arb.43 */44fun Arb.Companion.string(range: IntRange, codepoints: Arb<Codepoint> = Codepoint.ascii()): Arb<String> =45 Arb.string(range.first, range.last, codepoints)46/**47 * Returns an [Arb] where each random value is a String of length [size].48 * By default the arb uses a [ascii] codepoint generator, but this can be substituted49 * with any codepoint generator. There are many available, such as [katakana] and so on.50 *51 * There are no edge case values associated with this arb.52 */53fun Arb.Companion.string(size: Int, codepoints: Arb<Codepoint> = Codepoint.ascii()): Arb<String> =54 Arb.string(size, size, codepoints)55@Deprecated("This Shrinker does not take into account string lengths. Use StringShrinkerWithMin. This was deprecated in 4.5.")56object StringShrinker : Shrinker<String> {57 override fun shrink(value: String): List<String> {58 return when {59 value == "" -> emptyList()60 value == "a" -> listOf("")61 value.length == 1 -> listOf("", "a")62 else -> {63 val firstHalf = value.take(value.length / 2 + value.length % 2)64 val secondHalf = value.takeLast(value.length / 2)65 val secondHalfAs = firstHalf.padEnd(value.length, 'a')66 val firstHalfAs = secondHalf.padStart(value.length, 'a')67 val dropFirstChar = value.drop(1)68 val dropLastChar = value.dropLast(1)69 listOf(70 firstHalf,71 firstHalfAs,72 secondHalf,73 secondHalfAs,74 dropFirstChar,75 dropLastChar76 )77 }78 }79 }80}81/**82 * Shrinks a string. Shrunk variants will be shorter and simplified.83 *84 * Shorter strings will be at least [minLength] in length.85 *86 * Simplified strings will have characters replaced by a character (selected by [simplestCharSelector])87 * of each pre-shrunk value. By default, this is the first character of the pre-shrunk string.88 *89 * When [simplestCharSelector] returns null, no simpler variants will be created.90 */91class StringShrinkerWithMin(92 private val minLength: Int = 0,93 private val simplestCharSelector: (preShrinkValue: String) -> Char? = CharSequence::firstOrNull94) : Shrinker<String> {95// @Deprecated("a static 'simplestChar' means invalid shrinks can be generated - use the alternative constructor instead, which allows for a dynamic 'simplestChar'")96// constructor (97// minLength: Int = 0,98// simplestChar: Char,99// ) : this(minLength, { simplestChar })100 override fun shrink(value: String): List<String> {101 val simplestChar: Char? = simplestCharSelector(value)102 val isShortest = value.length == minLength103 val isSimplest = value.all { it == simplestChar }104 return buildList {105 if (!isShortest) {106 addAll(shorterVariants(value))107 }108 if (!isSimplest && simplestChar != null) {109 addAll(simplerVariants(value, simplestChar))110 }111 }.mapNotNull {112 // ensure the variants are at least minLength long113 when {114 simplestChar != null -> it.padEnd(minLength, simplestChar)115 it.length >= minLength -> it116 else -> null // this string is too short, so filter it out117 }118 }.distinct()119 }120 private fun simplerVariants(value: String, simplestChar: Char): List<String> =121 listOfNotNull(122 // replace the first and last chars that aren't simplestChar with simplestChar123 replace(value, simplestChar, value.indexOfFirst { it != simplestChar }),124 replace(value, simplestChar, value.indexOfLast { it != simplestChar }),125 )126 private fun shorterVariants(value: String) =127 listOf(128 value.take(value.length / 2 + value.length % 2),129 value.takeLast(value.length / 2),130 value.drop(1),131 value.dropLast(1),132 )133 private fun replace(value: String, newChar: Char, index: Int) =134 if (index == -1) null else value.replaceRange(index..index, newChar.toString())135}...

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1import io.kotest.matchers.shouldBe3import StringShrinkerWithMinUnitTest : FunSpec({7 test("should shrink the input") {8 checkAll(Arb.Companion.string(0, 4)) {9 }10 }11})

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