Assertj-core: UnknownFormatConversionException when asserting String with `%` sign

[asolntsev]

Summary

I have a test written in Kotlin. It throws UnknownFormatConversionException when I try to assert a String containing % character. The same test in Java works properly.

A hint: Java test calls method org.assertj.core.api.AbstractAssert#isEqualTo, while Kotlin test calls org.assertj.core.api.AbstractStringAssert#isEqualTo (which is buggie when there is no args).

Example

1. Test in Java - works:

import org.junit.Test;
import static org.assertj.core.api.Assertions.assertThat;

public class AssertJTest {
  @Test
  public void assertJ12() {
    assertThat("foo %").isEqualTo("foo %");
  }
}

1. The same test in Kotlin - fails:

import org.assertj.core.api.Assertions.assertThat
import org.junit.Test

class AssertJTest {
  @Test
  fun assertJ12() {
    assertThat("foo %").isEqualTo("foo %")
  }
}

Failure message is:

java.util.UnknownFormatConversionException: Conversion = '%'
    at java.base/java.util.Formatter.checkText(Formatter.java:2732)
    at java.base/java.util.Formatter.parse(Formatter.java:2718)
    at java.base/java.util.Formatter.format(Formatter.java:2655)
    at java.base/java.util.Formatter.format(Formatter.java:2609)
    at java.base/java.lang.String.format(String.java:2897)
    at org.assertj.core.api.AbstractStringAssert.isEqualTo(AbstractStringAssert.java:310)
    at controllers.api.AssertJTest.assertJ12(AssertJTest.kt:9)

[joel-costigliola]

@asolntsev Although your fix looks like to address the immediate issue, I wonder why is kotlin resolving isEqualTo(String template, Object... args) instead of isEqualTo(Object expected) ?

[joel-costigliola]

This issue is I believe the same as https://github.com/joel-costigliola/assertj-core/issues/1440#issuecomment-465032464

[asolntsev]

@asolntsev Although your fix looks like to address the immediate issue, I wonder why is kotlin resolving isEqualTo(String template, Object... args) instead of isEqualTo(Object expected) ?

Good question. I don't know. It's some specific of Kotlin.
Kotlin has a lot of surprises, you know :) Interoperability with Java is not as good as it should be :(

[maximusKon]

I guess Kotlin prefer to use function with more specific argument type.

[joel-costigliola]

@asolntsev @maximusKon As suggested by @epeee, would adding the following overload method to AbstractStringAssert solve the issue for kotlin users ?

public SELF isEqualTo(String s) {
  return super.isEqualTo(s);
}

If Kotlin chooses the method with the most specific arguments then I believe it should address the problem.

[asolntsev]

Probably. I need to check it.

On Sun, Mar 3, 2019, 11:50 Joel Costigliola [e-mail]
wrote:

@asolntsev https://github.com/asolntsev @maximusKon
https://github.com/maximusKon As suggested by @epeee
https://github.com/epeee, would adding the following overload method to
AbstractStringAssert solve the issue for kotlin users ?

public SELF isEqualTo(String s) {
return super.isEqualTo(s);
}

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[asolntsev]

@joel-costigliola @maximusKon @epeee
Yes, it also works!

I prepared an alternative PR for the same issue. Probably you find it better:
https://github.com/joel-costigliola/assertj-core/pull/1465

[kevcodez]

When do you plan to release this fix?

[joel-costigliola]

@kevcodez in a few weeks hopefully