content test: Compare parse trees via Diagnosticable

[gnprice]

I merged #205, and then a half-hour later saw a nicer way to do it. Better output on failure, and also less boilerplate code to write and update.

Happily none of the test cases change at all ­— only the infrastructure under them.

Before (if I artificially break one of the tests):

00:01 +16 -1: parse two plain-text paragraphs [E]                               
  Expected: a ZulipContent that:
    is a ZulipContent
    has nodes that:
      is deeply equal to (A value that:
        is a BlockContentNode
        is a ParagraphNode
        has wasImplicit that:
          equals <false>
        has nodes that:
          is deeply equal to (A value that:
            is a InlineContentNode
            equals <TextNode
               "hello">),
      A value that:
        is a BlockContentNode
        is a ParagraphNode
        has wasImplicit that:
          equals <false>
        has nodes that:
          is deeply equal to (A value that:
            is a InlineContentNode
            equals <TextNode
               "wrld">))
  Actual: a ZulipContent that:
    is a ZulipContent
    has nodes that:
    Actual: [ParagraphNode
     └─TextNode
         "hello",
    ParagraphNode
     └─TextNode
         "world"]
    Which: has an element at [<1>] that:
        is a BlockContentNode
        is a ParagraphNode
        has wasImplicit that:
          equals <false>
        has nodes that:
        Actual: [TextNode
           "world"]
        which has an element at [<0>] that:
          Actual: <TextNode
             "world">
          which are not equal
  package:checks/src/checks.dart 72:9                 check.<fn>
  package:checks/src/checks.dart 717:12               _TestContext.expect
  package:checks/src/extensions/iterable.dart 174:12  IterableChecks.deepEquals
  test/model/content_checks.dart 67:5                 BlockContentNodeListChecks.equalsNodes
  test/model/content_checks.dart 14:16                ContentNodeChecks.equalsNode
  test/model/content_test.dart 11:8                   testParse.<fn>
  

To run this test again: /home/greg/n/flutter/flutter/bin/cache/dart-sdk/bin/dart test /home/greg/z/flutterz/test/model/content_test.dart -p vm --plain-name 'parse two plain-text paragraphs'

After, with less noise and more information:

00:01 +16 -1: parse two plain-text paragraphs [E]                               
  Expected: a ZulipContent that:
    equals <ZulipContent
     ├─ParagraphNode
     │ └─TextNode
     │     "hello"
     │
     └─ParagraphNode
       └─TextNode
           "wrld">
  Actual: <ZulipContent
   ├─ParagraphNode
   │ └─TextNode
   │     "hello"
   │
   └─ParagraphNode
     └─TextNode
         "world">
  Which: differs in that it:
    has child 1 (ParagraphNode) that:
      has child 0 (TextNode) that:
        has text that:
          is 'world'
          expected: 'wrld'
  package:checks/src/checks.dart 72:9    check.<fn>
  package:checks/src/checks.dart 717:12  _TestContext.expect
  test/model/content_checks.dart 7:20    ContentNodeChecks.equalsNode
  test/model/content_test.dart 11:8      testParse.<fn>
  

To run this test again: /home/greg/n/flutter/flutter/bin/cache/dart-sdk/bin/dart test /home/greg/z/flutterz/test/model/content_test.dart -p vm --plain-name 'parse two plain-text paragraphs'

[chrisbobbe]

Great! Thanks; LGTM, merging.