wave I found a problem when doing an assertion on a nullable

Question

wave I found a problem when doing an assertion on a nullable variable e g ```nullableThing shouldBe something This works nullableThing shouldBeGreaterThan something This doesn t work``` If nullableThing is null the safe call stops the assertion from being called so the tests passes when it shouldn t I found two ways to fix this but neither seem ideal to me Add another assertion to check that the thing isn t null e g `nullableThing shouldNotBe null` Use ` ` instead of ` ` but this gives a null pointer exception when the test fails which could lead to confusion Is there a better way to deal with assertions on nullable variables

christophsturm · Answer

```val x String = blah x shouldNotBeNull x shouldBe blah ```

christophsturm · Answer

ok thats basically option one from your question i would recommend to do it like that

wasyl · Answer

Isn t `nullableThing something ` basically impossible to override It s compiler that is not calling `something` because that s how ` ` operator works blob thinking upside down

christophsturm · Answer

yes nullableThing does nothing when nullableThing is null so theres nothing to override but you can override Any something then you can do nullableThing something

Rob Elliot · Answer

You can use `shouldBe` on a nullable type Just use `nullableThing shouldBe something `

Rob Elliot · Answer

This works as expected for me ```val nullableThing String = null nullableThing shouldBe not null ``` ```Expected not null but actual was null java lang AssertionError Expected not null but actual was null```

phil-t · Answer

Thanks I ll give that a try

phil-t · Answer

Sorry I caused some confusion by simplifying my example code too much the matcher I was trying to use was `shouldBeGreaterThan` `shouldBe` and `shouldNotBe` work with nullable variables but `shouldBeGreaterThan` doesn t that causes this error `Only safe or non null asserted calls are allowed on a nullable receiver of type Int `

phil-t · Answer

Is there a reason why only certain matchers can handle nullables or is this something that could be added to other matchers

christophsturm · Answer

it just makes no sense to check if null is greater than 10 its neither greater nor lower than 10 but it makes sense to check it for equality its not equal to anything except null

christophsturm · Answer

so for things that make no sense to do with null you first assert that they are not null

phil-t · Answer

I see what you mean although I d argue that null is not greater than anything so that matcher could be altered to handle null and then it would give an error such as `null should be gt 0` The danger with the way it currently works is that it s too easy to try to fix the problem by using ` ` and then you have a test that will incorrectly pass when the variable is null

phil-t · Answer

Here s a similar thread where I tried to do this with strings <https kotlinlang slack com archives CT0G9SD7Z p1640084172325700>

sam · Answer

Some matchers work on nulls and some don t If you find one that doesn t but it should then a PR is welcome to fix it And a good workaround is that shouldNotBeNull can be chained so ```val name String = foo name shouldNotBeNull shouldHaveLength 3 ```

sam · Answer

most matchers should be chainable

phil-t · Answer

Cheers Sam I ve started chaining shouldNotBeNull in my tests and will have a look at fixing this in Kotest at some point will create an issue first

Michael Strasser · Answer

I have used a different style for potentially nullable things ```nullableThing let it shouldBe something fail thing should not be null ```