Test

The ShEx Test extension is a very simple extension intended for testing ShEx extension frameworks. Test participates in validate and has side-effects.

Example

The Test extension has two functions:

print(msg) - emit some mesage
fail(msg) - fail validation

Take a sample input schema with ShEx Test directives and input data:

PREFIX ex: <http://ex.example/#>
PREFIX foaf: <http://xmlns.com/foaf/>
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
PREFIX test: <http://shex.io/extensions/Test/>

%test:{  %}

start = <IssueShape>

<IssueShape> {
    ex:reportedBy @<UserShape>
        %test:{ fail("some message") %},
}

<UserShape> {
    foaf:name xsd:string
        %test:{ print(o) %}
}

PREFIX ex: <http://ex.example/#>
PREFIX foaf: <http://xmlns.com/foaf/>

<Issue1> ex:reportedBy <User2> .
<User2> foaf:name "Bob" .

In the ShEx Demo we see a failure:

<Issue1> matches <IssueShape>:
PASS {
  ex:reportedBy @<UserShape> %<http://shexspec.github.io/extensions/Test/>{ fail("some message") %} matched by <Issue1> ex:reportedBy <User2> .
    PASS {
Errors:
 ☹           eval of {"some message"} rejected [[
    <http://xmlns.com/foaf/name> <http://www.w3.org/2001/XMLSchema#string> %<http://shexspec.github.io/extensions/Test/>{ print(o) %} matched by <User2> <http://xmlns.com/foaf/name> "Bob".
    ]]
Matches:
      foaf:name xsd:string %<http://shexspec.github.io/extensions/Test/>{ print(o) %} matched by <User2> foaf:name "Bob" .
    }
}No remaining triples.

Examining the output (look for or link in validation messages) we see:

{
  "prints": [
    "Bob"
  ]
}

Definition

Test has a defined behavior when attached to a triple constraint. Other behaviors of Test are unspecified. There are two function in the Test extension:

print(msg) - emit some mesage
fail(msg) - fail validation

Each takes an argument, which is one of these four particles: s, p or o, or a literal delimited with "s and potentially containing "s and \s escaped by preceding \s.

For all SemActs, string literals are stripped of their delimiters, unescaped, and treated as a literal.
For SemActs on TripleExpressions, s, p and o correspond to the subject, predicate and object of the matching triple.
For SemActs on ShapeExpressions, s corresponds to focus node; the rest not defined.
For Start SemActs, no variable references are defined.

Parsing

Test directives can be parsed with the regular expression /^ *(fail|print) *$ *(?:("(?:[^\\"]|\\\\|\\")*")|([spo])) *$ *$/. The first capture group will be either "fail" or "print". The second will capture quoted strings, including their quotation marks. The third will captures the particles "s", "p", "o".

For any valid Test string, the first capture group and either the second or the third will be matched.

langauge	platform/API	package	source
javascript	shexjs	packaged	src

Issues

Test is not a practical extension (apart perhaps from debugging). It has side effects as well as participating in validation. The output when there is a failure is undefined. Some implementations, as the example above, may include the output even if validation failed. For these systems, print provides a print-debugging.