Things on this page are fragmentary and immature notes/thoughts of the author. Please read with your own judgement!

assert vs require vs assume

assert means that your program has reached an inconsistent state. This might be a problem with the current method/function (think of it a bit as e.g., HTTP 500 InternalServerError).

require means that the caller of the method is at fault and should fix its call (think of it a bit as e.g., HTTP 400 BadRequest). Use require whenever you want a constraint on parameters. Use assert whenever you want to make sure some conditions (like invariants) are always true during execution. It is a way of testing.

def assert(assertion: Boolean) { 
    if (!assertion) 
        throw new java.lang.AssertionError("assertion failed") 
} 

def assume(assumption: Boolean) { 
    if (!assumption) 
        throw new java.lang.AssertionError("assumption failed") 
} 

def require(requirement: Boolean) { 
    if (!requirement) 
        throw new IllegalArgumentException("requirement failed") 
} 

assert (java.lang.AssertionError) – a predicate which needs to be proven by a static code analyser to attempt to prove. It is something that you expect the static checker to be able to prove at compile time.

assume (java.lang.AssertionError) – an axiom for a static checker. It is something that the static checker can rely upon.

require (IllegalArgumentException) – Blames the caller of the method for violating the condition. Used as a pre-condition. ensuring is a post-condition.

scalaTest

1. It seems to be that scalaTest doesn't work well with junit5 at this time. The suggestion is to stick to junit4 when using scalaTest.

2. Java discourages the use of Singletons and unit testing on Singletons is not supported any more in JUnit5. However, due to the nature of functional programming, you will find Singletons to be nature in Scala.