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What FastCSV migration happened in JUnit 6 and what are the breaking changes?

JUnit 6 replaced the univocity-parsers library (used for CSV parsing in @CsvSource and @CsvFileSource) with FastCSV. This was necessary because univocity-parsers became unmaintained. FastCSV is faster and stricter, which causes a few breaking changes for tests with previously tolerated malformed CSV.

FastCSV migration breaking changes
ChangeJUnit 5 behaviourJUnit 6 behaviour
Extra characters after closing quoteSilently toleratedThrows exception: 'foo'INVALID,'bar' is invalid
lineSeparator attribute in @CsvFileSourceConfigurableRemoved: auto-detected (\r, \n, \r\n all work)
Header field processingignoreLeadingAndTrailingWhitespace etc. applied to data onlyNow apply to header fields as well
Comment character in @CsvSource# was default, no way to change itNew commentCharacter attribute; defaults to # but now configurable
Exception messages for malformed CSVImplementation-specificMay differ with FastCSV's error messages
// JUnit 5: this was silently tolerated (malformed CSV)
@CsvSource({"'foo'INVALID,'bar'"})
void test(String a, String b) { ... }
// ^ JUnit 6: throws exception -- extra chars after closing quote

// JUnit 6: lineSeparator removed -- auto-detected
// JUnit 5:
@CsvFileSource(resources = "/data.csv", lineSeparator = "\n")
// JUnit 6:
@CsvFileSource(resources = "/data.csv")  // lineSeparator attribute gone

// JUnit 6: new commentCharacter attribute (needed if # appears in data)
@CsvSource(value = {
    "#this is a comment -- skipped",
    "1, 2, 3",
}, commentCharacter = '#')
void additionTest(int a, int b, int expected) { ... }

// Conflicting delimiter bug fix (from 6.0.1):
// A regression in 6.0.0 caused exception when delimiter=# in @CsvSource
// because # was ALSO the comment character with no way to override.
// 6.0.1 added commentCharacter attribute to fix this.

Why did JUnit 6 replace univocity-parsers with FastCSV?
What happened to the lineSeparator attribute of @CsvFileSource in JUnit 6?

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