1. A method comprising: obtaining, by a computer system including one or more computers, a first set of test values, a second set of test values, and a third set of test values; receiving, by the computer system, text comprising characters represented as code point values, the characters identified as being in a first encoding format, each code point value representing one character in the text; and making a determination by the computer system that the text likely includes characters incorrectly converted from a second encoding format to the first encoding format, wherein making the determination includes (i) determining for a sequence of code point values consisting of a first code point value followed by a second code point value that the first code point value is in the first set of test values and that the second code point value is in the second set of test values, or (ii) determining for a sequence of code point values consisting of a first code point value followed by a second code point value followed by a third code point value that the first code point value is in the third set of test values, that the second code point value is in the second set of test values, and that the third code point value is in the second set of test values.