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Something like "Power assert" in Scala similar to Groovy?

I'm wondering if there is something that can give me results similar to Groovy's nice power assert statement.

> assert ["1", '2']*.size() == [2, 3]

Result: Assertion failed: 

assert ["1", '2']*.size() == [2, 3]
                   |      |
                   [1, 1] false

AFAIK there is no support for such thing neither in language, nor in scalatest, which I'm currently using. But maybe someone can suggest some side library doing that? It's a pet project, so experimental and not well-supported libs are fine.

EDIT: I know about matchers (scalatest ones, or even plain-java hamcrest matchers). I find them verbose to write and that their output lacks details.

The example above shows intermediate computation steps, facilitating detection of errors. It shows you what's wrong with tested code with more details.

I expect, that introducing such behaviour will require having information about expression AST at runtime. But I suppose, that this information can be "baked" compile time with usage of macroses.

I.e. if we have expression assert a + b == c scala (or some macro extension I'm looking for) can rewrite it to something like:

if (!(a + b == c)) {
  // detailed message is
  // compute a
  // compute b
  // compute a + b
  // compute c
  // compute a + b == c
  // Make it pretty.

  throw new AssertionFailedException(prettyDetailedMessage)
}

So I'm looking if it's already implemented, and if yes - where.

Solution

  • In ScalaTest, you can use DiagrammedAssertions. See http://www.scalatest.org/release_notes/2.2.0#diagrammedAssertions

    This is based on Expecty which is a macro-based implementation of Spock's power assertions. See https://github.com/pniederw/expecty