expect-kt

expect-kt is a set of fluent assertions for Kotlin, for a better readability of your code than using kotlin.test. Each type has a set of extension functions that allow you to check certain specifics that relate to that type.

This project is a fork of https://github.com/kouphax/expect.kt. That project was abandoned (since 2012 without commits) and lacking a way to use with Gradle/maven. I updated it so I can use on some projects, and hope to improve some areas and add new features (like better messages and new extensions).

This is too a way for me to understand Kotlin and explore its features. The original project was inspired by FluentAssertions for .NET and now I’m inpired by AssertJ too.

Table of Contents

• Gradle dependency
• Syntax
  • Expect Syntax
  • Fluent Syntax
• Chaining
• Standard Assertions
  • toBe/be
  • toNotBe/notBe
  • toBeNull/beNull
  • toNotBeNull/notBeNull
  • toBeInstanceOf/beInstanceOf
• Logic Assertions
  • toBeTrue/beTrue
  • toNotBeTrue/notBeTrue
  • toBeFalse/beFalse
  • toNotBeFalse/notBeFalse
• String Assertions
  • toBeEmpty/beEmpty
  • toNotBeEmpty/beNotEmpty
  • toHaveLength/haveLength
  • toBeBlank/beBlank
  • toNotBeBlank/notBeBlank
  • toBeEquivalentTo/beEquivalentTo
  • toStartWith/startWith
  • toStartWithEquivalent/startWithEquivalent
  • toEndWith/endWith
  • toEndWithEquivalent/endWithEquivalent
  • toContain/contain
  • toContainEquivalent/containEquivalent
  • toNotContain/notContain
  • toNotContainEquivalent/notContainEquivalent
  • toMatch/match
• Numeric Assertions (currently Int, Long, Double, Float)
  • toBeGreaterOrEqualTo/beGreaterOrEqualTo
  • toBeGreaterThan/beGreaterThan
  • toBeLessOrEqualTo/beLessOrEqualTo
  • toBeLessThan/beLessThan
  • toBeInRange/beInRange
  • toBeApproximately/beApproximately
• Collection Assertions (currently List)
  • toBeEmpty
  • toNotBeEmpty
  • toHaveSize
  • toHaveSameSizeAs
  • toContain
  • toContainAll
  • toContainNull
  • toNotContainNull
  • toNotContain
  • toNotContainAny
  • anyToMatchLambda
  • allToMatchLambda
  • noneToMatchLambda
  • toStartWith
  • toEndWith
  • toHaveItemAt
  • toHaveInstanceOfItemAt
  • toNotContainDuplicates
  • toBeSubsetOf
• Extending expect-kt

Gradle dependency

Add expect-kt as a test dependency

dependencies {
    testImplementation 'com.tsuharesu:expect-kt:0.9.0'
}

Syntax

expect-kt allows you to use two different approaches to define an assertion:

Expect Syntax

Expect syntax offers typical expect(something).toBeInACertainState style of grammar that everybody uses. Like this:

expect("james").toBe("james")

Fluent Syntax

It is also possible to use a more fluent syntax (some kind of BDD) to make the same assertion

"james".should.be("james")

Chaining

expect-kt allows you to chain assertions to keep things really neat and tidy.

expect("james").toStartWith("j").and.toEndWith("s")

Or, in fluent syntax.

"james".should.startWith("j").and.endWith("s")

Or using blocks, because sometimes you want lots of checks.

expect("james") {
    toStartWith("j")
    toEndWith("s")
}

"james".should {
    startWith("j")
    endWith("s")
}

Standard Assertions

There are a few assertions that can be used on any type

toBe/be

Assert that the value should be equal to the other

expect("james").toBe("james")
"james".should.be("james")

toNotBe/notBe

Assert that the value should NOT be equal the other

expect("james").toNotBe("jaime")
"james".should.notBe("jaime")

toBeNull/beNull

Assert that the value is null

expect(null).toBeNull()
null.should.beNull()

toNotBeNull/notBeNull

Assert that the value is NOT null

expect("james").toNotBeNull()
"james".should.notBeNull()

toBeInstanceOf/beInstanceOf

Assert that the value should of some class.

expect("james").toBeInstanceOf(String::class)
expect(SomeTestClass()).toBeInstanceOf(SomeTestClass::class)
"james".should.beInstanceOf(String::class)

It does not work very well with numbers (Int, Float, …)

Logic Assertions

toBeTrue/beTrue

Assert that the value is true

expect(true).toBeTrue()
true.should.beTrue()

toNotBeTrue/notBeTrue

Assert that the value is NOT true

expect(false).toNotBeTrue()
false.should.notBeTrue()

toBeFalse/beFalse

Assert that the value is false

expect(false).toBeFalse()
false.should.beFalse()

toNotBeFalse/notBeFalse

Assert that the value is NOT false

expect(true).toNotBeFalse()
true.should.notBeFalse()

String Assertions

toBeEmpty/beEmpty

Assert that a string is empty ("")

expect("").toBeEmpty()
"".should.beEmpty()

toNotBeEmpty/beNotEmpty

Assert that a string is NOT empty ("")

expect("  ").toNotBeEmpty()
"  ".should.beNotEmpty()

toHaveLength/haveLength

Assert that a string is of a certain length

expect("james").toHaveLength(5)
"james".should.haveLength(5)

toBeBlank/beBlank

Assert that a string is blank, in that it is empty or contains only whitespace

expect("   ").toBeBlank()
"    ".should.beBlank()

toNotBeBlank/notBeBlank

Assert that a string is not blank, in that it isn’t empty or contains more than whitespace

expect("james").toNotBeBlank()
"james".should.notBeBlank()

toBeEquivalentTo/beEquivalentTo

Assert that a string is equal to another string regardless of case (ignore case comparation)

expect("JAMES").toBeEquivalentTo("james")
"JAMES".should.beEquivalentTo("james")

toStartWith/startWith

Assert that a string starts with another string.

expect("james").toStartWith("j")
"james".should.startWith("j")

toStartWithEquivalent/startWithEquivalent

Assert that a string starts with another string regardless of case.

expect("james").toStartWithEquivalent("JA")
"james".should.startWithEquivalent("JA")

toEndWith/endWith

Assert that a string ends with another string

expect("James").toEndWith("es")
"James".should.endWith("es")

toEndWithEquivalent/endWithEquivalent

Assert that a string ends with another string regardless of case

expect("JAMES").toEndWithEquivalent("es")
"JAMES".should.endWithEquivalent("es")

toContain/contain

Assert that a string contains another string

expect("james").toContain("am")
"james".should.contain("am")

toContainEquivalent/containEquivalent

Assert that a string contains another string regardless of case.

expect("JAMES").toContainEquivalent("am")
"JAMES".should.containEquivalent("am")

toNotContain/notContain

Assert that a string doesn’t contain another string.

expect("james").toNotContain("ei")
"james".should.notContain("ei")

toNotContainEquivalent/notContainEquivalent

Assert that a string doesn’t contain another string regardless of case.

expect("JAMES").toNotContainEquivalent("ei")
"JAMES".should.notContainEquivalent("ei")

toMatch/match

Assert that a string matches the given regex.

expect("james").toMatch(Regex("^james$"))
"james".should.match(Regex("^james$"))

Numeric Assertions (currently Int, Long, Double, Float)

toBeGreaterOrEqualTo/beGreaterOrEqualTo

Assert that a number is greater than or equal to another

expect(2).toBeGreaterOrEqualTo(1)
2.should.beGreaterOrEqualTo(1)

toBeGreaterThan/beGreaterThan

Assert that a number is greater than to another

expect(2).toBeGreaterThan(1)
2.should.beGreaterThan(1)

toBeLessOrEqualTo/beLessOrEqualTo

Assert that a number is less than or equal to another

expect(1).toBeLessOrEqualTo(2)
1.should.beLessOrEqualTo(2)

toBeLessThan/beLessThan

Assert that a number is less than to another

expect(1).toBeLessThan(2)
1.should.beLessThan(2)

toBeInRange/beInRange

Assert that a number is within the lower and upper bounds passed in

expect(2).toBeInRange(1, 3)
2.should.beInRange(1, 3)

toBeApproximately/beApproximately

Assert that a number is approximately another - the level of error is defined by the tolerance value (+/- tolerance)

expect(2f).toBeApproximately(2.1f, 0.1f)
2f.should.beApproximately(2.1f, 0.1f)

Collection Assertions (currently List)

toBeEmpty

Assert that the list don’t have any items

expect(listOf<String>()).toBeEmpty()
listOf<String>().should.beEmpty()

toNotBeEmpty

Assert that the list contain items

expect(listOf("james")).toNotBeEmpty()
listOf("james").should.notBeEmpty()

toHaveSize

Assert that the list contains x items

expect(listOf("james", "cindy")).toHaveSize(2)
listOf("james", "cindy").should.haveSize(2)

toHaveSameSizeAs

Assert that the list contains the same of items as other list (same type or not)

expect(listOf("james", "cindy")).toHaveSameSizeAs(listOf(1, 2))
listOf("james", "cindy").should.haveSameSizeAs(listOf(1, 2))

toContain

Assert that the list contains this item

expect(listOf("james", "cindy")).toContain("james")
listOf("james", "cindy").should.contain("james")

toContainAll

Assert that the list contains all this items

expect(listOf("james", "cindy")).toContainAll(listOf("james"))
listOf("james", "cindy").should.containAll(listOf("james"))

toContainNull

Assert that the list contains a null value

expect(listOf("james", null)).toContainNull()
listOf("james", null).should.containNull()

toNotContainNull

Assert that the list does not contain null

expect(listOf("james", "cindy")).toNotContainNull()
listOf("james", "cindy").should.notContainNull()

toNotContain

Assert that the list does not contain this item

expect(listOf("james", "cindy")).toNotContain("tsu")
listOf("james", "cindy").should.notContain("tsu")

toNotContainAny

Assert that the list does not contain any of these items

expect(listOf("james", "cindy")).toNotContainAny(listOf("tsu"))
listOf("james", "cindy").should.notContainAny(listOf("tsu"))

anyToMatchLambda

Assert that the list contains any item that matches the lambda (predicate)

expect(listOf(1, 2)).anyToMatchLambda { it > 1 }
listOf(1, 2).should.anyMatchLambda { it > 1 }

allToMatchLambda

Assert that all items in the list matches the lambda (predicate)

expect(listOf(2, 4, 6)).allToMatchLambda { it.mod(2) == 0 }
listOf(2, 4, 6).should.allMatchLambda { it.mod(2) == 0 }

noneToMatchLambda

Assert that the list does not have any item that matches the lambda (predicate)

expect(listOf(1, 2)).noneToMatchLambda { it > 2 }
listOf(1, 2).should.noneMatchLambda { it > 2 }

toStartWith

Assert that the list first item is this

expect(listOf("james", "cindy")).toStartWith("james")
listOf("james", "cindy").should.startWith("james")

toEndWith

Assert that the list last item is this

expect(listOf("james", "cindy")).toEndWith("cindy")
listOf("james", "cindy").should.endWith("cindy")

toHaveItemAt

Assert that the list have a specific item at a position

expect(listOf("james", "cindy")).toHaveItemAt("cindy", 1)
listOf("james", "cindy").should.haveItemAt("cindy", 1)

toHaveInstanceOfItemAt

Assert that the list contains an instance of this class at that index

expect(listOf("james", 1)).toHaveInstanceOfItemAt(String::class, 0)
listOf("james", 1).should.haveInstanceOfItemAt(String::class, 0)

toNotContainDuplicates

Assert that the list does not contains duplicated items

expect(listOf("james", "cindy")).toNotContainDuplicates()
listOf("james", "cindy").should.notContainDuplicates()

toBeSubsetOf

Assert that this list is a subset of another list

expect(listOf("james", "cindy")).toBeSubsetOf(listOf("james", "cindy", "tsu", "aphrodite"))
listOf("james", "cindy").should.beSubsetOf(listOf("james", "cindy", "tsu", "aphrodite"))

Extending expect-kt

Expectations in expect-kt are extension functions to Expectation and Should . If you want a expectation function that don’t already exist, you can create one in your files as this:

fun Expectation<Type>.toBeSomething(something: Type): ExpectationChain<Type> {
    assertTrue(target.doSomething())
    return ExpectationChain(this)
}

fun Should<Type>.beSomething(something: Type): ShouldChain<Type> {
    expectation.toBeSomething(value)
    return ShouldChain(this)
}

Where:

• Type is the class you are testing. For example: Int, String, User (your own class), List<T>

• target is the object of Type that your expectation will run against

• Your method should return a ExpectationChain/ShouldChain for that type, so you can chain your calls

• Your method can receive any number and any type of parameters

• Should extensions usually just call Expectation methods because Should is a sugar around Expectation anyway.

You can check CustomExpectationTests.kt to see an example.