How to use AssertThat to check the property value of objects in a list?

Question

I am to using asserThat to verify properties of objects in an ArrayList.

I am able to use assertThat if none of the objects contains data to be tested but I am not able to figure how to use assertThat if only one of the objects contain data to be tested.

Sample Code:

public class dataNeeded {
    String data;
    String modifiedDate;

    public String getData(){
         return data;
    }
    ......
}

public ArrayList<dataNeeded> returnsNeededData(){
 ...
}

List<dataNeeded> dataToBeTested = returnsNeededData();
dataToBeTested.forEach(data->assertThat(data.getData(), not(equalTo("No"))));

List<dataNeeded> dataToBeTested2 = returnsNeededData();
// I need to verify if one of the objects in this list has it's data as "No" 
dataToBeTested.forEach(data->assertThat(data.getData(), ???);

Answer 1

You can map to List<String> via the following function (uses Java 8 Streams) to extract all data strings

private List<String> mapToDataStrings(List<dataNeeded> neededData) {
    return neededData.stream()
            .map(dataNeeded -> dataNeeded.getData())
            .collect(toList());
}

and then use the everyItem/hasItem function in Matchers to make assertions on the resulting list of strings:

List<String> dataToBeTested = mapToDataStrings(returnsNeededData());
assertThat(dataToBeTested, everyItem(not("No")));

List<String> dataToBeTested2 = mapToDataStrings(returnsNeededData());
assertThat(dataToBeTested2, hasItem("No"));

With everyItem you can assert that every element in the list is not "No" and hasItem asserts that there is at least one element in the list with value "No".

---

Alternatively you could implement a feature matcher to avoid the mapping function.