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Michael Baas edited this page May 25, 2022 · 9 revisions

(introduced with v1.70)

Assert can be used to write tests as you may know them from other environments. The function verifies that ⍺≡⍵ and will signal an event so that the test-fn immediately ends. There are several options to pass a message to the environment about the error:

  • the easiest way to document a failing Assert is by adding a comment to the line that contains the Assert statement. The error message will show the line with the failing test, so it'll be directly commented:
sink←1 Assert 0.5+0.4   ⍝ this should not fail with value 0.5+0.5!

The result of DTest will then be:

       test_assert: Test returned character value = "Assertion failed: ERROR 777        
       test_assert[6] sink←1 Assert 0.5+0.4   ⍝ this should not fail with value 0.5+0.5!
  • if the line would get too long when a comment is added, you can also place the comment in the line immediately preceding or following the test and it will be shown in the result as well:
       test_assert: Test returned character value = "Assertion failed:  this should not fail with value 0.5+0.5!
       test_assert[7] sink←1 Assert 0.5+0.4
  • finally, the reason for a failing test may not be "static" as in the examples before, but it could be given in a variable (ie. you call a fn and test its returncode. If it is non-zero, you want to display a msg that was generated by the fn you called). In that case, use ⊢ to separate variable and test:
       MyMsg⊢0 Assert rc:

Notice that this excerpt from a test that was written as a dfn, features an "empty guard" - they are a valid construct within dfns! (The MyMsg⊢ part obviously has no effect on the result, but is an optional "notational tweak" that enables Assert to create a meaningful message about the reason of a failed assertion!) DTest will report the failing test as shown:

 test_assert: Test returned character value = "Assertion failed: Error msg computed elsewhere...                               
       test_assert[12] MyMsg⊢1 Assert 2×0.4:

(the text "Error msg computed elsewhere..." is the actual content of MyMsg!)

If an assertion fails and the -halt modifier was set when ]DTest was called, the execution of Assert will halt after detecting the difference and you then have an opportunity to inspect the environment.

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