Missing formats for --list_content #397

There are currently 2 formats for --list_content:

1. The human-readable format, great visually finding a test
2. The dot format, great for visualizing the test-suite

Over the years, I found 2 formats to be missing:

List of test-cases

For simple tools or integration with external test runners like CTest, it would be super useful to have an output listing all testcases in an easy to consume way:

testsuite1/testcase1
testsuite1/testcase2
testsuite2/testcase3

Generating this information from the existing formats is rather tedious.

Use cases:

• Register testcases as separate tests external test runners, such as CTest
• Writing custom tools that work only on test cases, such as bisection of test cases, running them with GNU parallel, or running them individually in various docker containers.
• Use fuzzy search to quickly find a testcase and run it ./test --list_content=LIST | fzf | xargs ./test -t

Detailed machine-readable output

For advanced tools, a detailed dump of the test tree would be useful.
JSON would be suitable as it can easily be generated without special libraries.

{
  "type": "suite",
  "name": "testsuite1",
  "fileName": "...",
  "fileLine": 21,
  "labels": [],
  "children": [
    {
      "type": "case",
      "name": "testcase1",
      "fileName": "...",
      "fileLine": 23,
      "labels": []
    },
    {
      "type": "case",
      "name": "testcase2",
      "fileName": "...",
      "fileLine": 33,
      "labels": []
    }
  ]
}

The DOT format includes some of this information in a less structured way as most of it is encoded in the label.

Use cases:

• Custom linters
• Merging the detailed test setup with external data
• Intermediate format to generate other custom formats