Modern C++ Programming with Test-Driven Development

2.13 Doing What It Takes to Clarify Tests

For our next test, we tackle the case where two adjacent letters encode to the same digit. Per Soundex rule #3, such duplicate letters get encoded as a single digit. The rule also states that it applies to the first letter. Let’s deal with the first case now and worry about the first letter next.

TEST_F(SoundexEncoding, CombinesDuplicateEncodings) {
   ASSERT_THAT(soundex.encode("Abfcgdt"), Eq("A123"));
}

That’s a confusing test! To understand why ​Abfcgdt​ encodes to ​A123​, we have to know that ​b​ and ​f​ both encode to ​1​, ​c​ and ​g​ both encode to ​2​, and ​d​ and ​t​ both encode to ​3​. We can learn these facts from reading other tests, such as ReplacesConsonantsWithAppropriateDigits, ...