Update tests bird watcher

[jagdish-15]

pull request

This would catch solutions like these:

    public int[] getLastWeek() {
        return birdsPerDay;
    }

    public void incrementTodaysCount() {
        for (int i = 1; i < birdsPerDay.length; i++) {
            birdsPerDay[i] = birdsPerDay[i] + 1;
        }
    }

Variants like this have appeared in student solutions and currently pass the tests, even though they don’t align with the exercise instructions

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[kahgoh]

This is going to invalidate solutions that return the array in getLastWeek, like this one.

If our objective is to just capture the incrementTodaysCount, I think we could just change itIncrementTodaysCount.

[kahgoh]

Ah, this is a clever way (using getCountForFirstDays). Just couple of minor comments for this one:

• We could simplify this by doing calculating the expected value directly, like we currently do in the other test for getCountForFirstDays (i.e. assertThat(birdWatcher.getCountForFirstDays(6)).isEqualTo(DAY1 + DAY2 + DAY3 + DAY4 + DAY5 + DAY6);).
• I think it can be confusing why we're asserting getCountForFirstDays in this test. I'd suggest moving to a separate test so that the test can be described in the @DisplayName and test name. For example:

public void itIncrementDoesNotChangeCountForOtherDays() {
  birdWatcher.incrementTodaysCount();
  assertThat(birdWatcher.getCountForFirstDays(6)).isEqualTo(DAY1 + DAY2 + DAY3 + DAY4 + DAY5 + DAY6);
}