See issue #2123. HLOOKUP needs to do some conversions between column numbers and letters which it had not been doing.
HLOOKUP tests were performed using direct calls to the function in question rather than in the context of a spreadsheet. This contributed to keeping this error obscured even though there were, in theory, sufficient test cases. The tests are changed to perform in spreadsheet context. For the most part, the test cases are unchanged. One of the expected results was wrong; it has been changed, and a new case added to cover the case it was supposed to be testing.
After getting the HLOOKUP tests in order, it turned out that a test using literal arrays which had been succeeding now failed. The array constructed by the literals are considerably different than those constructed using spreadsheet cells; additional code was added to handle this situation.
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