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A language agnostic test suite for TOML encoders and decoders

toml-test is a higher-order program that tests other TOML decoders or encoders. The goal is to make it comprehensive. Tests are divided into two groups: invalid TOML data and valid TOML data. Decoders that reject invalid TOML data pass invalid TOML tests. Deocoders that accept valid TOML data and output precisely what is expected pass valid tests. The output format is JSON, described below.

Both decoders and encoders share valid tests, except an encoder accepts JSON and outputs TOML. The TOML representations are read with a blessed decoder and compared. Note though that encoders have their own set of invalid tests in the invalid-encoder directory. The JSON given to a TOML encoder is in the same format as the JSON that a TOML decoder should output.

Version: v0.4.0 (in sync with TOML)

Compatible with TOML version v0.4.0

Dependencies: Go.

Try it out

All you need is to have Go installed. Then simply use:

export GOPATH=$HOME/go # if it isn't already set
go get # install test suite
go get # e.g., install my parser
$HOME/go/bin/toml-test $HOME/go/bin/toml-test-decoder # e.g., run tests on my parser
# Outputs: 64 passed, 0 failed

The go get commands install Go packages and binaries into your GOPATH.

To test your decoder, you will have to satisfy the interface expected by toml-test described below. Then just execute toml-test your-decoder in the toml-test directory to run your decoder against all tests.

To test your encoder, the instructions are the same, except the input/output is reversed, and you'll need to run toml-test -encoder your-encoder. (You can install my TOML encoder with go get

Interface of a decoder

For your decoder to be compatible with toml-test, it must satisfy the interface expected.

Your decoder must accept TOML data on stdin until EOF.

If the TOML data is invalid, your decoder must return with a non-zero exit code indicating an error.

If the TOML data is valid, your decoder must output a JSON encoding of that data on stdout and return with a zero exit code indicating success.

Interface of an encoder

For your encoder to be compatible with toml-test, it must satisfy the interface expected.

Your encoder must accept JSON data on stdin until EOF.

If the JSON data cannot be converted to a valid TOML representation, your encoder must return with a non-zero exit code indicating an error.

If the JSON data can be converted to a valid TOML representation, your encoder must output a TOML encoding of that data on stdout and return with a zero exit code indicating success.

JSON encoding

The following JSON encoding applies equally to both encoders and decoders.

  • TOML tables correspond to JSON objects.
  • TOML table arrays correspond to JSON arrays.
  • TOML values correspond to a special JSON object of the form {"type": "{TTYPE}", "value": {TVALUE}}

In the above, TTYPE may be one of:

  • string
  • integer
  • float
  • datetime
  • bool
  • array

and TVALUE is always a JSON string, except when TTYPE is array in which TVALUE is a JSON array containing TOML values.

Empty hashes correspond to empty JSON objects (i.e., {}) and empty arrays correspond to empty JSON arrays (i.e., []).

Datetime should be encoded following RFC 3339.

Example JSON encoding

Here is the TOML data:

best-day-ever = 1987-07-05T17:45:00Z

boring = false
perfection = [6, 28, 496]

And the JSON encoding expected by toml-test is:

  "best-day-ever": {"type": "datetime", "value": "1987-07-05T17:45:00Z"},
  "numtheory": {
    "boring": {"type": "bool", "value": "false"},
    "perfection": {
      "type": "array",
      "value": [
        {"type": "integer", "value": "6"},
        {"type": "integer", "value": "28"},
        {"type": "integer", "value": "496"}

Note that the only JSON values ever used are objects, arrays and strings.

Assumptions of Truth

The following are taken as ground truths by toml-test:

  • All tests classified as invalid are invalid.
  • All tests classified as valid are valid.
  • All expected outputs in valid/test-name.json are exactly correct.
  • The Go standard library package encoding/json decodes JSON correctly.
  • When testing encoders, the TOML decoder at BurntSushi/toml is assumed to be correct. (Note that this assumption is not made when testing decoders!)

Of particular note is that no TOML decoder is taken as ground truth when testing decoders. This means that most changes to the spec will only require an update of the tests in toml-test. (Bigger changes may require an adjustment of how two things are considered equal. Particularly if a new type of data is added.) Obviously, this advantage does not apply to testing TOML encoders since there must exist a TOML decoder that conforms to the specification in order to read the output of a TOML encoder.

Adding tests

toml-test was designed so that tests can be easily added and removed. As mentioned above, tests are split into two groups: invalid and valid tests.

Invalid tests only check if a decoder rejects invalid TOML data. Or, in the case of testing encoders, invalid tests only check if an encoder rejects an invalid representation of TOML (e.g., a hetergeneous array). Therefore, all invalid tests should try to test one thing and one thing only. Invalid tests should be named after the fault it is trying to expose. Invalid tests for decoders are in the tests/invalid directory while invalid tests for encoders are in the tests/invalid-encoder directory.

Valid tests check that a decoder accepts valid TOML data and that the parser has the correct representation of the TOML data. Therefore, valid tests need a JSON encoding in addition to the TOML data. The tests should be small enough that writing the JSON encoding by hand will not give you brain damage. The exact reverse is true when testing encoders.

A valid test without either a .json or .toml file will automatically fail.

If you have tests that you'd like to add, please submit a pull request.


In order for a language agnostic test suite to work, we need some kind of data exchange format. TOML cannot be used, as it would imply that a particular parser has a blessing of correctness.

My decision to use JSON was not a careful one. It was based on expediency. The Go standard library has an excellent encoding/json package built in, which made it easy to compare JSON data.

The problem with JSON is that the types in TOML are not in one-to-one correspondence with JSON. This is why every TOML value represented in JSON is tagged with a type annotation, as described above.

YAML may be closer in correspondence with TOML, but I don't believe we should rely on that correspondence. Making things explicit with JSON means that writing tests is a little more cumbersome, but it also reduces the number of assumptions we need to make.

Decoders or encoders that satisfy the toml-test interface

If you have an implementation, send a pull request adding to this list. Please note the commit SHA1 or version tag that your parser supports in your README.

N.B. Your decoder/encoder doesn't need to pass all tests to be on this list.

TOML projects using the test suite

I'm not sure why, but some projects seem to build their own testing harness while using the tests in this repository. That's OK, but it's probably more work than necessary. Plus, I claim that toml-test outputs nice error messages.


A language agnostic test suite for TOML parsers.




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