How to check if element in groovy array/hash/collection/list?

Some syntax sugar

1 in [1,2,3]

.contains() is the best method for lists, but for maps you will need to use .containsKey() or .containsValue()

[a:1,b:2,c:3].containsValue(3)
[a:1,b:2,c:3].containsKey('a')