resistor-color-duo and property tests

[sshine]

After #865, resistor-color-duo's value :: (Color, Color) -> Int is ideal for property testing.

Some properties that can be tested:

• value (Black, x) < 10 for all x
• value (x, y) >= 10 for all x except Black and all y
• show (value (x, y)) == reverse (show (value (y, x))) for all x, y except Black.
• (Color, Color) is isomorphic to [0..99] (or: all colors have a unique value).
• Associativity: Kind of tricky because you can't get the value of a single Color:

  value (k, x) <= value (k, y) && value (k, y) <= value (k, z)
    ⇒ value (k, x) <= value (k, z)
  
  value (x, k) <= value (y, k) && value (y, k) <= value (z, k)
    ⇒ value (k, x) <= value (k, z)
  

Considering how simple this exercise is, adding all these property tests with the purpose to aid students is slightly overkill. (It could use a few more unit tests for basic coverage, though.)

So I thought: Why not encourage property testing in .meta/hints.md?

In the style of #843, add one or two property tests and encourage others.

A pull request that proposes this awaits for #865 to merge.

[chiroptical]

So I thought: Why not encourage property testing in .meta/hints.md?

Basically, you want to show the student how to write a QuickCheck property test and then suggest a few properties to test? (with links to documentation etc?)

[sshine]

Yes, that was my thought.

[sshine]

@barrymoo: If you'd like, #865 has now been merged and this issue is ready to be worked on.

[chiroptical]

@sshine I was going to work on this today, but I noticed the Hints section is no longer displayed on the exercism website? Cases where we have implemented the Data.Text library aren't mentioned.

[sshine]

@barrymoo: Thank you for noticing!

@iHiD: Can you explain why #865, which was merged a month ago, which adds a hint to the README and updates test/Tests.hs, does not get updated on the website? Is this a bug, or is there a precondition that I'm not aware of?

[iHiD]

Hello. It's there for me when I go to the track anew and check. Maybe you're versions of the exercise are out of date? Do you see the button to click to update it?

[chiroptical]

@iHiD Updating worked for me. I am hoping to work on this soon!