Let's say I have two Quantity objects q1 and q2, both with metric == Metric.UNIT and

• q1.amount equal to new BigDecimal("1.0"), and
• q2.amount equal to new BigDecimal("1").

(Note that the two BigDecimal objects are not equal as per BigDecimal.equals().)

Now I compare q1 and q2 using assertThat(q1).isEqualTo(q2). This fails with the following error message:

org.opentest4j.AssertionFailedError: 
Expecting:
 <"1 (Quantity@5acf93bb)">
to be equal to:
 <"1 (Quantity@7e7be63f)">
but was not.

The misleading identical output of actual vs. expected is because the current toString() always strips trailing zeroes. (By the way, the objects are considered unequal because they use an exact comparison of amount, instead of BigDecimal.compareTo().)

I suggest to:

• include the canonical representation of amount (as returned by BigDecimal.toString()), making it easier to spot the difference, and
• complete the compareTo()-like feature set of Quantity by adding isEqualTo() to the already existing isGreaterThan(), isLessThan(), etc.

Using BigDecimal.compareTo() instead of BigDecimal.equals() in Quantity.equals() is probably not an option because of inconsistencies with hashCode().