Cannot cast BooleanAssert to Boolean when using assertj-core:3.25.3 StringAssert's in a Spock then block

[ocindev]

Describe the bug

In the 3.25.3 release of assertj-core a feature was added that allows any StringAssert to be interpreted and asserted as a boolean value through the AbstractStringAssert#asBoolean() method. asBoolean() returns a BooleanAssert instance to allow further method chaining with boolean assertions.

The then block in a Spock test feature wraps any assertion code line with a Groovy Power Assert assert under the hood and expects the actual assertion to be evaluated as a boolean value.
This conflicts with the Groovy built-in org.codehaus.groovy.runtime.DefaultGroovyMethods#asBoolean(java.lang.Object) that Spock is using on anything that is not a Boolean value.

In the end this produces ClassCastExceptions for any usage of StringAssert from assertj.

To Reproduce

import spock.lang.Specification

import static org.assertj.core.api.Assertions.assertThat

class DemoSpec extends Specification {
    def 'assert some integer'() {
        when:
        def someInteger = 10

        then:
        assertThat(someInteger).isEqualTo(10)
    }

    def 'assert some string'() {
        when:
        def someString = 'some string'

        then:
        assertThat(someString).isEqualTo('some string')
    }
}

Expected behavior

All tests are successful.

Actual behavior

The assert some string feature fails due to a ClassCastException - BooleanAssert cannot be casted to Boolean.

Java version

openjdk 17.0.10 2024-01-16
OpenJDK Runtime Environment Temurin-17.0.10+7 (build 17.0.10+7)
OpenJDK 64-Bit Server VM Temurin-17.0.10+7 (build 17.0.10+7, mixed mode)

Buildtool version

---

Gradle 8.6

Build time: 2024-02-02 16:47:16 UTC
Revision: d55c486870a0dc6f6278f53d21381396d0741c6e

Kotlin: 1.9.20
Groovy: 3.0.17
Ant: Apache Ant(TM) version 1.10.13 compiled on January 4 2023
JVM: 17.0.10 (Eclipse Adoptium 17.0.10+7)
OS: Mac OS X 14.2.1 aarch64

What operating system are you using

Mac

Dependencies

• org.apache.groovy:groovy-all:4.0.18
• org.spockframework:spock-core
• org.spockframework:spock-bom:2.3-groovy-4.0
• org.spockframework:spock-junit4
• org.assertj:assertj-core:3.25.3

Additional context

No response

[AndreasTu]

Can you expain the reason, why you want to write:

then:
assertThat(someInteger).isEqualTo(10)
assertThat(someString).isEqualTo('some string')

instead of:

then:
someInteger == 10
someString == 'some string'

The Spock power asserts are shorter to write and have a better error message than the AssertJ assertions.

Note: Since 2.4-M2: If you want to suppress the assertion you can write !! before a line to prevent assertions.

then:
!!assertThat(someInteger).isEqualTo(10)

See Opt-out of condition handling for details.

[AndreasTu]

Also here is a reproducer without AssertJ dependency:

class DemoSpec extends Specification {
    def 'assert some string'() {
        when:
        def o = new TestAssertStub()

        then:
        o.func()
    }
    
    static class TestAssertStub{
        TestAssertStub func(){
            return this
        }
        
        String asBoolean(){
            return "STR"
        }
    }
}

Throws:

java.lang.ClassCastException: class java.lang.String cannot be cast to class java.lang.Boolean

[AndreasTu]

I am really not sure here, because this also break, when Spock is not involved, but only Groovy:

def o = new TestAssertStub()
assert o.func()

class TestAssertStub{
    TestAssertStub func(){
        return this
    }

    String asBoolean(){
        return "STR"
    }
}

AssertJ does not play well here with the Groovy sematic to use the method asBoolean() to convert it to a boolean.

Maybe we can fix the spock part when such a thing is used in a then: block,
but the general issue when combined with a normal Groovy assert can't be solved by Spock.
I also commented that on the original issue in the AssertJ repo.

[leonard84]

I don't think there is anything for us to fix, as @AndreasTu already pointed out we have the opt-out operator, but in this particular case the asBoolean conflicts with Groovy's default methods.

[scordio]

@leonard84 @AndreasTu I'd be happy to get your thoughts on assertj/doc#167.