The assertion parts tuple defining the assertion structure
// For assertion: expect(value, 'to be a string')
type Subject = ParsedSubject<Parts>; // typeof value
// For assertion: expect(42, 'to be greater than', 10)
type NumericSubject = ParsedSubject<NumericParts>; // number
Type extracting the subject (first argument) from parsed assertion values.
This utility type extracts the subject of an assertion from the parsed values tuple. The subject is always the first element and represents the value being tested by the assertion.