Custom Assertions

mechmind edited this page Nov 15, 2013 · 2 revisions

Sometimes a test suite might need an assertion that is too specific to be included in the general repository. Not to worry, simply implement a function with the following signature (replace the bracketed parts and string values):

func should<do-something>(actual interface{}, expected ...interface{}) string {
    if <some-important-condition-is-met(actual, expected)> {
        return ""   // empty string means the assertion passed
    } else {
        return "<some descriptive message detailing why the assertion failed...>"

Suppose I implemented the following assertion:

func shouldScareGophersMoreThan(actual interface{}, expected ...interface{}) string {
    if actual == "BOO!" && expected[0] == "boo" {
        return ""
    } else {
        return "Ha! You'll have to get a lot friendlier with the capslock if you want to scare a gopher!"

I can then make use of the assertion function when calling the So() method in the tests:

Convey("All caps always makes text more meaningful", func() {
    So("BOO!", shouldScareGophersMoreThan, "boo")


If you haven't figured out how already, it's time to learn how to run your tests.