Hspec Expectations for JSON Values

Comparing JSON Values in Haskell tests comes with some challenges:

• In API responses, additive changes are typically safe and an important way to evolve responses without breaking clients. Therefore, assertions against such responses often want to ignore any unexpected keys in Objects (at any depth), as any clients would.

• Order often doesn't matter in API responses either, so it should be possible to assert equality regardless of Array ordering (again, at any depth).

• When an assertion fails, showing the difference clearly needs to take the above into account (i.e. it can't show keys you've ignored, or ordering differences you didn't care about), and it has to display things clearly, e.g. as a diff.

This library handles all these things.

Usage

NOTE: this is effectively a distillation of the Haddocks, please view them directly for your installed version, to ensure accurate information.

Four expectations exist with the following behaviors:

Assertion that fails on:	extra Object keys	wrong Array order
shouldBeJson	Yes	Yes
shouldBeUnorderedJson	Yes	No
shouldMatchJson	No	No
shouldMatchOrderedJson	No	Yes

Each of these, when they fail, print a difference between the objects, where the expected-on object has been normalized to avoid indicating any of the differences your expectation is ignoring.

shouldBeJson

Passing:

catchFailure $
  [aesonQQ| { "a": true, "b": false } |] `shouldBeJson`
  [aesonQQ| { "a": true, "b": false } |]

Failing:

catchFailure $
  [aesonQQ| { "a": true, "b": false } |] `shouldBeJson`
  [aesonQQ| { "a": true, "b": true  } |]

   {
       "a": true,
---    "b": true
+++    "b": false
   }

shouldBeUnorderedJson

Passing:

catchFailure $
  [aesonQQ| { "a": [true, false], "b": false } |] `shouldBeUnorderedJson`
  [aesonQQ| { "a": [false, true], "b": false } |]

Failing:

catchFailure $
  [aesonQQ| { "a": [true, false], "b": false, "c": true } |] `shouldBeUnorderedJson`
  [aesonQQ| { "a": [false, true], "b": true             } |]

   {
       "a": [
           false,
           true
       ],
---    "b": true
+++    "b": false,
+++    "c": true
   }

shouldMatchJson

Passing:

catchFailure $
  [aesonQQ| { "a": [true, false], "b": false, "c": true } |] `shouldMatchJson`
  [aesonQQ| { "a": [false, true], "b": false            } |]

Failing:

catchFailure $
  [aesonQQ| { "a": [true, false], "b": false, "c": true } |] `shouldMatchJson`
  [aesonQQ| { "a": [false, true], "b": true             } |]

   {
       "a": [
           false,
           true
       ],
---    "b": true
+++    "b": false
   }

shouldMatchOrderedJson

Passing:

catchFailure $
  [aesonQQ| { "a": [true, false], "b": false, "c": true } |] `shouldMatchOrderedJson`
  [aesonQQ| { "a": [true, false], "b": false            } |]

Failing:

catchFailure $
  [aesonQQ| { "a": [true, false], "b": false, "c": true } |] `shouldMatchOrderedJson`
  [aesonQQ| { "a": [false, true], "b": true             } |]

   {
       "a": [
---        false,
---        true
+++        true,
+++        false
       ],
---    "b": true
+++    "b": false
   }

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