Implement `testSimple` assertion operator that only outputs head expression

[stephen-swensen]

The output from test can be verbose and distracting, especially when it includes large object graphs. Provide a "simple" assertion operator (call it testSimple) that provides a less noisy alternative. The behavior of test should not be changed, because it is generally useful.

See discussion in https://github.com/SwensenSoftware/unquote/pull/134

Depends on https://github.com/SwensenSoftware/unquote/issues/133 - decompiling and reducing ValueWithName expressions - to be effective

Given a test setup and assertion like the following

type Foo = { Foo : string ; Bar : int }
let x = { Foo = "foo" ; Bar = 41 }
testSimple <@ x.Bar = 42 @>

Produce output like the following:

Option A (just output the head expression)

Test failed:

x.Bar = 42

Option B (just output the head and last expression; skip intermediate reductions)

Test failed:

x.Bar = 42
41 = 42
false

[stephen-swensen]

@eiriktsarpalis any preference on Option A vs. Option B? I'm partial to Option B because to me it appears to provide the two most important pieces of information given by the regular test operator but without the noise of the intermediate reduction steps: the source assertion expression and the final reduction (well, the final two reduction - the second to last one is the interesting one here; we'd preserve false just for closer symmetry to test). I suppose the appeal of Option A would be just to have a truly stripped down, source assertion only decompilation.

[eiriktsarpalis]

The main issue with B seems to be that it can blow up in certain cases, e.g. performing structural equality checks on large values. Just emitting the initial tree should provide sufficient context to the test author for establishing what went wrong.

[stephen-swensen]

@eiriktsarpalis that's fair - Option A it is. Thinking about it more, anyone who'd be more interested in Option B would probably just go with the usual test in the first place.

[stephen-swensen]

https://github.com/SwensenSoftware/unquote/pull/146/commits/d6712d096337446f39773b339ccdf96588e03f1d

[stephen-swensen]

@eiriktsarpalis FYI - this is released as part of Unquote 5.0.0 today!