message: Add tests for Array::front()/back()
diff: @@ -556,6 +556,7 @@ void check_insert_iterator(Array<T>& v)
  capacity = calc_new_capacity(v, 1);
  typename axom::Array<T>::ArrayIterator ret3 = v.insert(v.begin(), 1, i);
  EXPECT_EQ(ret3, v.begin());
  + EXPECT_EQ(i, v.front());
  size++;
  }
  @@ -641,6 +642,7 @@ void check_emplace(Array<T>& v)
  capacity = calc_new_capacity(v, 1);
  typename axom::Array<T>::ArrayIterator ret3 = v.emplace(v.begin(), i);
  EXPECT_EQ(ret3, v.begin());
  + EXPECT_EQ(i, v.front());
  size++;
  }
  @@ -1235,7 +1237,9 @@ TEST(core_array, checkIterator)
  }
  EXPECT_EQ(*v_int.begin(), 0);
  + EXPECT_EQ(v_int.front(), 0);
  EXPECT_EQ(*(v_int.end() - 1), SIZE - 1);
  + EXPECT_EQ(v_int.back(), SIZE - 1);
  EXPECT_EQ(v_int.size(), SIZE);
  /* Erase nothing */
  @@ -1251,7 +1255,9 @@ TEST(core_array, checkIterator)
  EXPECT_EQ(ret2, v_int.begin());
  EXPECT_EQ(*v_int.begin(), SIZE / 2);
  + EXPECT_EQ(v_int.front(), SIZE / 2);
  EXPECT_EQ(*(v_int.end() - 1), SIZE - 1);
  + EXPECT_EQ(v_int.back(), SIZE - 1);
  EXPECT_EQ(v_int.size(), SIZE / 2);
  /* Erase first, last elements */
  @@ -1259,11 +1265,13 @@ TEST(core_array, checkIterator)
  EXPECT_EQ(ret3, v_int.begin());
  EXPECT_EQ(*v_int.begin(), SIZE / 2 + 1);
  + EXPECT_EQ(v_int.front(), SIZE / 2 + 1);
  axom::Array<int>::ArrayIterator ret4 = v_int.erase(v_int.end() - 1);
  EXPECT_EQ(ret4, v_int.end());
  EXPECT_EQ(*(v_int.end() - 1), SIZE - 2);
  + EXPECT_EQ(v_int.back(), SIZE - 2);
  /* Clear the rest of the array */
  v_int.clear();
  