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How to Write a Custom Tester

Custom Class

A custom tester can be used to run multiuple tests. The custom tester is a Class that extends AbstractCustomTester. It needs a runTests() function that returns a boolean.

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Private Class DateTimeTester As AbstractCustomTester

    Function runTests As Boolean

        Dim dateTime As Variant
        Dim mon As Integer

        Call Me.testSuite.checkStarted()

        dateTime = CDat(|30/01/2022|)
        Call checkIsDateTime(Datetime)

        mon = Month(dateTime)
        checkMonthLessThan13(mon)

        Call Me.testSuite.describe(|Check dateTime is before Now|).assertIsLessThan(Now(), CDbl(dateTime))

    End Function

End Class

This is a custom class extending AbstractCustomTester. The only function we need to add is runTests(). The function can return a boolean if successful. But here, the outer code is only interested in whether or not the TestSuite ran successfully, which the TestSuite class handles internally. So no return value is passed out of the function.

This is the first test for the TestSuite, so on line 8, we call the checkStarted function of the TestSuite, which is a property of the parent class. This sets the timer for the TestSuite and, if appropriate, runs a custom beforeAll() function. We then call two internal functions - checkIsDateTime() and checkMonthLessThan13() and finally run an inline assertion. These are:

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Function checkIsDateTime(dateTime As Variant) As Boolean
    checkIsDateTime = Me.testSuite.describe(|Check is DateTime Variant|).assertIs(|DATE|, dateTime)
End Function

Function checkMonthLessThan13(mon As Integer)

    Try
        Call Me.testSuite.describe(|Check month is less than 13|)
        If (mon < 13) Then
            Call Me.testSuite.addResult(True, "")
            checkMonthLessThan13 = True
        Else
            Call Me.testSuite.addResult(False, "Expected less than 13, was " & mon)
            checkMonthLessThan13 = False
        End If
    Catch
        Call testSuite.addError(testSuite.getErrorMsg, GetThreadInfo(12))
    End Try

End Function

The first function runs a simple assertion. The second one is more complex. A result is added (true or false), with the appropriate message. If there is an error - which should not happen in this scenario - the test is errored.

Using the Class

Using the class is very straightforward. We create a TestSuite and an instance of the custom tester class. We then add the TestSuite to the tester and call the tester's runTests() function.

Dim TestSuite As New TestSuite(|DateTime Tests|)
Dim DateTimeTester As New DateTimeTester

Call DateTimeTester.addTestSuite(TestSuite).runTests()

If we wished, additional tests could be run before or after calling the tester's runTests() function.