Shazamcrest

'Shazamcrest' is a library that extends the functionality of hamcrest.

Assertions on complete beans are made simpler by serialising the actual and expected beans to json, and comparing the two. The diagnostics are leveraging the comparison functionality of IDEs like Eclipse or IntelliJ.

Usage

Having a Person bean with the following structure:

Person person
    |-- String name
    |-- String surname
    |-- Address address
        |-- String streetName
        |-- int streetNumber
        |-- String postcode

to compare two Person beans with Shazamcrest we would write:

assertThat(actualPerson, sameBeanAs(expectedPerson));

instead of explicitly match every field of the bean and sub-beans:

assertThat(actualPerson, allOf(
        hasProperty("name", equalTo(expectedPerson.name)),
        hasProperty("surname", equalTo(expectedPerson.surname)),
        hasProperty("address", allOf(
            hasProperty("streetName", equalTo(expectedPerson.address.streetName)),
            hasProperty("streetNumber", equalTo(expectedPerson.address.streetNumber)),
            hasProperty("postcode", equalTo(expectedPerson.address.postcode)))
        )
    ));

Error Messages

If the person address streetName does not match the expectations, the following diagnostic message is displayed:

org.junit.ComparisonFailure: address.streetName
        Expected: Via Roma
    got: Via Veneto
        expected:<... "streetName": "Via [Roma]",
    "streetNumber...> but was:<... "streetName": "Via [Veneto]",
    "streetNumber...>

The exception thrown is a ComparisonFailure which can be used by IDEs like Eclipse and IntelliJ to display a visual representation of the differences.

Note: in order to get the ComparisonFailure on mismatch the "assertThat" to use is com.shazam.shazamcrest.MatcherAssert.assertThat rather than org.hamcrest.MatcherAssert.assertThat

Ignoring fields

If we are not interested in matching the street name, we can ignore it by specifying the field path:

assertThat(actualPerson, sameBeanAs(expectedPerson).ignoring("address.streetName"));

If we want to match the address only by the postcode, we can ignore street name and number by specifying the fields name pattern:

assertThat(actualPerson, sameBeanAs(expectedPerson).ignoring(startsWith("street")));

where startsWith is an Hamcrest matcher.

Custom matching

If we want to make sure that the street name starts with "Via" at least:

assertThat(actualPerson, sameBeanAs(expectedPerson).with("address.streetName"), startsWith("Via"));

Circular references

Having a Shop bean with the following structure:

Shop shop
	|-- String name
    |-- Store store
        |-- Boss boss
            |-- Clerk clerk
                |-- Store store
                |-- Boss boss

Comparing two Shop objects throws a StackOverflowError, because of the cycles Clerk -> Store -> Boss -> Clerk and Clerk -> Boss -> Clerk.

From version 0.10 the circular reference is detected automatically and the serialiser is instructed to serialise the instance once and replace all the other occurrences with a pointer:

assertThat(actualShop, sameBeanAs(expectedShop));

produces the following representation:

{
  "store": {
    "0x1": {
      "0x1": {
        "0x1": {
          "boss": "0x2"
        }
      }
    },
    "0x2": {
      "0x1": {
        "0x1": {
          "clerk": {
            "boss": "0x2",
            "store": "0x1"
          }
        }
      }
    }
  },
  "name": "shop"
}

QuickStart

To use, download the zip or add the following to your project's pom.xml:

<dependency>
    <groupId>com.shazam</groupId>
    <artifactId>shazamcrest</artifactId>
    <version>0.11</version>
</dependency>