Added test for finding literal triples

[jesper-friis]

Description:

Added test for finding literal triples.

That works, but it turned out that we need to support untyped literals. See issue #182

Type of change:

• Bug fix and code cleanup.
• New feature.
• Documentation update.
• Testing.

Checklist for the reviewer:

This checklist should be used as a help for the reviewer.

• Is the change limited to one issue?
• Does this PR close the issue?
• Is the code easy to read and understand?
• Do all new feature have an accompanying new test?
• Has the documentation been updated as necessary?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.47%. Comparing base (c18a9f1) to head (614736e).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #183      +/-   ##
==========================================
+ Coverage   77.40%   77.47%   +0.07%     
==========================================
  Files          17       18       +1     
  Lines        1540     1545       +5     
==========================================
+ Hits         1192     1197       +5     
  Misses        348      348              

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