Testing Data Serialisation/Deserialization in Java (with Jackson)
When working with data models in Java, we'll often have a Plain Old Java Object (POJO) that corresponds to the incoming request body, so we can interact with it more easily and have access to getters/setters.
Because this is a pretty integral part of interacting with other services / being interacted with, we need to make sure these models are mapped correctly.
Testing these can be done in a few ways, but often I see them not being tested as low in the test pyramid as we can do.
Fortunately, there are a few options for how we can test that serialisation (from object to string) and deserialisation (from string to object) works.
For instance, let's say we have the class:
/**
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as
* published by the Free Software Foundation, either version 3 of the
* License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonInclude.Include;
import com.fasterxml.jackson.annotation.JsonProperty;
public class TokenGrantDto {
@JsonProperty("access_token")
@JsonInclude(Include.NON_NULL)
private String accessToken;
@JsonProperty("refresh_token")
@JsonInclude(Include.NON_NULL)
private String refreshToken;
private long expiresIn;
@JsonProperty("token_type")
@JsonInclude(Include.NON_NULL)
private String tokenType;
@JsonInclude(Include.NON_NULL)
private String scope;
@JsonInclude(Include.NON_NULL)
private String me;
public String getAccessToken() {
return accessToken;
}
public void setAccessToken(String accessToken) {
this.accessToken = accessToken;
}
public String getRefreshToken() {
return refreshToken;
}
public void setRefreshToken(String refreshToken) {
this.refreshToken = refreshToken;
}
@JsonInclude(Include.NON_NULL)
@JsonProperty("expires_in")
public Long getExpiresIn() {
if (0 == expiresIn) {
return null;
}
return expiresIn;
}
public void setExpiresIn(long expiresIn) {
this.expiresIn = expiresIn;
}
public String getTokenType() {
return tokenType;
}
public void setTokenType(String tokenType) {
this.tokenType = tokenType;
}
public String getScope() {
return scope;
}
public void setScope(String scope) {
this.scope = scope;
}
public String getMe() {
return me;
}
public void setMe(String me) {
this.me = me;
}
}
This then may have a unit or unit integration test like the following, which uses Jackson's ObjectMapper to verify serialisation/deserialisation:
/**
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as
* published by the Free Software Foundation, either version 3 of the
* License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
import static org.assertj.core.api.Assertions.assertThat;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.node.ObjectNode;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Nested;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.ValueSource;
class TokenGrantDtoTest {
private static final ObjectMapper mapper = new ObjectMapper();
private ObjectNode node;
@Nested
class Serialization {
@Nested
class HappyPath {
@BeforeEach
void setup() throws JsonProcessingException {
TokenGrantDto dto = new TokenGrantDto();
dto.setAccessToken("j.w.t");
dto.setRefreshToken("j.w.t.2");
dto.setExpiresIn(1234L);
dto.setMe("https://me");
dto.setScope("draft update");
dto.setTokenType("Bearer");
String actual = mapper.writeValueAsString(dto);
node = mapper.readValue(actual, ObjectNode.class);
}
@Test
void accessTokenIsMapped() {
assertThat(node.get("access_token").textValue()).isEqualTo("j.w.t");
}
// ommitted for brevity
@Test
void expiresInIsMapped() {
assertThat(node.get("expires_in").numberValue()).isEqualTo(1234L);
}
}
// ommitted for brevity
@Nested
class WhenMissingProperties {
@BeforeEach
void setup() throws JsonProcessingException {
TokenGrantDto dto = new TokenGrantDto();
String actual = mapper.writeValueAsString(dto);
node = mapper.readValue(actual, ObjectNode.class);
}
@ParameterizedTest
@ValueSource(strings = {"access_token", "expires_in", "me", "scope", "token_type"})
void propertiesAreNotMapped(String property) {
assertThat(node.get(property)).isNull();
}
}
}
}
This gives us a pretty handy test harness!
