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luhn: add a test case #1246

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May 29, 2018
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luhn: add a test case #1246

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10 changes: 9 additions & 1 deletion exercises/luhn/canonical-data.json
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Original file line number Diff line number Diff line change
@@ -1,6 +1,6 @@
{
"exercise": "luhn",
"version": "1.1.0",
"version": "1.2.0",
"cases": [
{
"description": "single digit strings can not be valid",
Expand Down Expand Up @@ -105,6 +105,14 @@
"value": "091"
},
"expected": true
},
{
"description": "strings with non-digits is invalid",
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How is this new case different from "valid strings with a non-digit included become invalid"?

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@idealhack idealhack May 25, 2018 •
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package luhn

import "strings"

func Valid(str string) bool {
	str = strings.Replace(str, " ", "", -1)
	if len(str) < 2 {
		return false
	}

	var sum = 0
	for i, ch := range str {
		val := int(ch - '0')
		if (len(str)-i)%2 == 0 {
			product := val * 2
			if product > 9 {
				product -= 9
			}
			sum += product
		} else {
			sum += val
		}
	}

	return sum%10 == 0
}

The code with a mistake above will pass current tests, but not this one.

So we have to check non-digits by adding:

if val > 9 || val < 0 {
    return false
}

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Thanks for the explanation. I can see now how "valid strings with a non-digit included become invalid" passes without the new test case.

Other reviewers may ask that your new test case be moved to an earlier location in the JSON file. I'll leave that open to others to address.

@idealhack thanks for your time in improving this exercise! 👍

"property": "valid",
"input": {
"value": ":9"
},
"expected": false
}
]
}