The following test:

        for (Object[] test : new Object[][] {
            {"Long.MAX_VALUE",Long.MAX_VALUE},
            {"Long.MAX_VALUE-1",Long.MAX_VALUE-1},
            {"1",1L},
            {"0", 0L},
            {"-1",-1L},
            {"Long.MIN_VALUE+1",Long.MIN_VALUE+1},
            {"Long.MIN_VALUE",Long.MIN_VALUE}
            }) {

            long millis = (Long)test[1];
            System.err.println("Testing with " + test[0] +": "+millis+"L");
            Instant i1 = Instant.ofEpochMilli(millis);
            System.err.println("Instant.ofEpochMilli(): " + i1);
            long seconds = i1.getEpochSecond();
            System.err.println("Instant.getEpochSecond(): " + seconds);
            System.err.println("millis/1000: " + millis/1000);

            long millis2 = i1.toEpochMilli();
            System.err.println("Instant.toEpochMilli(): " + millis2+"L");
            if (millis2 != millis) {
                throw new RuntimeException("Test failed for " + test[0]
                        + "\n\texpected: "+millis+"L"
                        + "\n\tactual: "+millis2+"L");
            }
        }

causes an arithmetic overflow for Long.MIN_VALUE+1 and Long.MIN_VALUE.

Exception in thread "main" java.lang.ArithmeticException: long overflow
at java.lang.Math.multiplyExact(Math.java:915)
at java.time.Instant.toEpochMilli(Instant.java:1232)