ZIO Test: Support Labeled Assertions

[adamgfraser]

In some cases it can be useful to label assertions to provide additional information for test reporting. For example, consider the following test:

testM("test") {
  for {
    a <- ZIO.effectTotal(Some(1))
    b <- ZIO.effectTotal(Some(1))
    c <- ZIO.effectTotal(Some(0))
    d <- ZIO.effectTotal(Some(1))
  } yield assert(a, isSome(equalTo(1)) &&
    assert(b, isSome(equalTo(1)) &&
    assert(c, isSome(equalTo(1)) &&
    assert(d, isSome(equalTo(1))
}

This test will fail with an error message that "0 did not satisfy equalTo(1)", but that is not particularly helpful here because we don't know which of the four composed assertions failed. This PR adds a method label to Assertion that labels an assertion with an arbitrary string. Using this, the test could be rewritten as:

testM("test") {
  for {
    a <- ZIO.effectTotal(Some(1))
    b <- ZIO.effectTotal(Some(1))
    c <- ZIO.effectTotal(Some(0))
    d <- ZIO.effectTotal(Some(1))
  } yield assert(a, isSome(equalTo(1)).label("first")) &&
    assert(b, isSome(equalTo(1)).label("second")) &&
    assert(c, isSome(equalTo(1)).label("third")) &&
    assert(d, isSome(equalTo(1)).label("fourth"))
}

The error message would now get reported like so:

[jdegoes]

Might suggest ?? instead of @@ to match ZIO Config; and also have ?? operator alias.

[adamgfraser]

Great! Will change now.