import re
test_string = "test_string TEST_STRING TEST_string _TEST_STRING_ TESTSTRING ANOTHER_TEST_STRING"
p = re.compile(r"\b[A-Z]+_[A-Z_]*[A-Z]\b")
print(re.findall(p,test_string))
aW1wb3J0IHJlCnRlc3Rfc3RyaW5nID0gInRlc3Rfc3RyaW5nIFRFU1RfU1RSSU5HIFRFU1Rfc3RyaW5nIF9URVNUX1NUUklOR18gVEVTVFNUUklORyBBTk9USEVSX1RFU1RfU1RSSU5HIgpwID0gcmUuY29tcGlsZShyIlxiW0EtWl0rX1tBLVpfXSpbQS1aXVxiIikgCnByaW50KHJlLmZpbmRhbGwocCx0ZXN0X3N0cmluZykp