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Dhall Acceptance Tests

This folder contains the "acceptance tests suite" for the Dhall language.
This means that while the tests are not part of the standard per se, a standard-compliant implementation is expected to successfully manage through all the tests here.
If this is not the case, then one of the following holds:

  1. the implementation is not standard-compliant
  2. the implementation is standard-compliant but the standard is underspecified and the other implementations are relying on some assumption. This should be considered a bug of the specification and the assumption in question should be added to the standard
  3. the implementation is standard-compliant and there's a bug in the tests. This should be considered a bug for the test suite

Please open an issue if you stumble on either 2. or 3.

How to run these tests

The tests are split by the feature that they are testing (we generally aim to test only one feature at a time) into different folders: normalization, type-inference, etc. (Please see the next sections on more details on what to do for every test suite)

Inside each of them, the tests are split by the expected result:

  • success: there is always two files for each test case:
    • ${TestcaseName}A.dhall is the expression to evaluate
    • ${TestcaseName}B.dhall is the result that the interpreter is supposed to return
  • failure: the interpreter is expected to error out when evaluating each test case
  • other folders at the same depth level - like data - can be ignored, as they only contain data to support the other tests.

At the next depth level (that is, inside success, etc) tests are grouped by some other common feature they might have. This split is not functionally relevant (unlike the previous two), but just to keep things tight.
Some common subdivisions at this level:

  • prelude: test for the Prelude
  • simple: tests that only exercise the feature in question (e.g. normalization contains some tests which require the import system to work correctly, except for the ones categorized as simple, which don't depend on the import system being implemented)

But how should every feature be exercised? The following sections detail what to run for each feature:

Running parser tests

The tests should:

  • parse A and encode it to its binary CBOR representation
  • read B as bytes
  • the results should match

Where A and B are:

  • A: a Dhall expression as text
  • B: the binary representation of the Dhall-CBOR-encoded expression

Note: Each B.dhallb file has a matching B.diag file containing the CBOR diagnostic notation for the encoded expression. You can generate the .diag file using the ./scripts/generate-test-files.sh script and our continuous integration will remind you to do so (by failing if you don't keep the diagnostic file up-to-date).

Running normalization tests

The tests should:

  • parse A and B
  • eventually resolve the imports in both (if not running simple or unit tests)
  • normalize A (but not B)
  • the results should match

Where A and B are:

  • A: unnormalized text
  • B: normalized text

Running alpha-normalization tests

The tests should:

  • parse A and B
  • α-normalize them both
  • the results should match

Where A and B are:

  • A: unnormalized text
  • B: normalized text

Running semantic-hash tests

The tests should:

  • parse A
  • eventually resolve the imports (if not running simple tests)
  • compute the semantic hash of A (hash of binary after both alpha and beta normalization)
  • the hash should be equal to what is found in B

Running type-inference tests

Note: if your implementation does not implement typechecking correctly, some of the type-inference/failure tests may not terminate. This is because typechecking is central to Dhall's guarantees of totality: only expressions which typecheck are guaranteed to terminate. As a result, you may want to guard against nontermination, such as by adding a timeout to these tests.

The tests should:

  • parse A and B
  • if not running simple or unit tests, resolve the imports in A without using the cache
  • infer the type of A
  • the inferred type of A should exactly match B

Where A and B are:

  • A: unnormalized text
  • B: type of A

(Note: for the failure tests we just expect typecheck failure)

Running import tests

You must run these tests in such a way that they can read cache entries from dhall-lang/tests/import/cache/dhall as if it were the Dhall cache. For example, on unix systems you could set the environment variable XDG_CACHE_HOME to the absolute location of dhall-lang/tests/import/cache. This is so that we can test that an import with an integrity check is fetched from cache (for example, see hashFromCacheA.dhall). Your tests should not make persistent writes to this cache – for example, you could:

  • treat this cache directory as read-only, or
  • reset the cache after test runs to discard any writes your implementation does (for example, run git clean -f tests/import/cache), or
  • copy the cache to a fresh temporary directory for each test run.

You must run these tests in such a way that the home directory ~ is set to the dhall-lang/tests/import/home/ directory. For example, on unix systems you could set the environment HOME to the absolute location of the dhall-lang/tests/import/home/ directory. On windows the environment variable would be %USERPROFILE%.

You should make it so that the environment variable DHALL_TEST_VAR is set to the string "6 * 7". This enables testing importing from environment variables.

Some test cases have a ${TestcaseName}ENV.dhall file, containing a Text map, i.e., a value of type List { mapKey: Text, mapValue: Text }. If present, you should read the ${TestcaseName}ENV.dhall file, beta-normalize it, obtain the given environment names and values from the resulting mapKeys and mapValues, and resolve the test expression with the given environment variables set.

The tests should:

  • parse A and B
  • resolve the imports for both A and B, in a context with a single ancestor consisting of the relative path from the parent directory of this repository to the test file (for example: ./dhall-lang/tests/import/success/asLocationA.dhall)
  • the results should match

Where A and B are:

  • A: text with unresolved imports
  • B: text where all the imports have been resolved, normalized and replaced with their value

The ancestor ensures that the as Location tests chain in the expected way.

Running binary-decode tests

The tests should:

  • decode A from the Dhall binary encoding
  • parse B
  • the results should match

Where A and B are:

  • A: binary encoded Dhall expression
  • B: text of the equivalent Dhall expression