This tests UTF-8 decoding. Namely, it checks that all valid codepoints are properly decoded; even the ones that are illegal characters. The first test is the important one; this library should only generate legal codepoints.

For completeness, a second test that includes the surrogate pair range [0xD800-0xDFFF] is also included. Interestingly, different browsers appear to have different policies with respect to substituting these illegal codepoints.