Modern C++ Programming with Test-Driven Development

2.12 Dropping Vowels

Rule #1 says to drop all occurrences of vowels and the letters ​w​, ​h​, and ​y​. For lack of a better name, we’ll refer to these as ​ vowel-like​ letters.

TEST_F(SoundexEncoding, IgnoresVowelLikeLetters) {
   ASSERT_THAT(soundex.encode("Baeiouhycdl"), Eq("B234"));
}

The test passes without us adding a lick of production code, because ​encodedDigit​ answers an empty string if the letter to be encoded wasn’t found. Any vowels thus encode to the empty string, which gets harmlessly appended.

​A test that passes with no change to your classes is always cause for humility and pause (see Section 3.5, ​Getting Green on Red​).​ Ask yourself, “What might I have done differently?”

If a stream of subsequent ...