While testing WT-11332, I ended up having a truncated output from the Python tests because of the following hardcoded value:
    def checkAdditionalPattern(self, testcase, pat, re_flags = 0):
...
        gotstr = self.readFileFrom(self.filename, self.expectpos, 1500)
We should be more flexible on the number of characters we want to read. For instance, the functions readStdout and readStderr have this flexibility:
    def readStdout(self, maxchars=10000):
        return self.captureout.readFileFrom(self.captureout.filename, self.captureout.expectpos, maxchars)
    def readStderr(self, maxchars=10000):
        return self.captureerr.readFileFrom(self.captureerr.filename, self.captureerr.expectpos, maxchars)