java - How to unit test JSON parsing

Question

I'm working on an Android app in which I download JSON data from a web service. The class parsing the data looks something like this:

public class JsonCourseParser implements CourseParser {

    public Course parseCourse(String courseData) {
        Course result;

        try {
            JSONObject jsonObject = new JSONObject(courseData);

            ...

            result = new Course("foo", "bar");
        } catch (JSONException e) {
            result = null;
        }

        return result;
    }
}

This builds just fine and it works when I call parseCourse() from within my app, but when I try to test this method in a unit test I get this exception:

java.lang.NoClassDefFoundError: org/json/JSONException
    at JsonCourseParserTest.initClass(JsonCourseParserTest.java:15)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:27)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:236)
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:49)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)
Caused by: java.lang.ClassNotFoundException: org.json.JSONException
    at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
    ... 16 more

It seems that the classes of the org.json package which come with the Android Framework are not available in Java by default.

Is there a way I can fix this so I can unit test the classes which parse JSON?

Answer 1

All you need to do is add the following line to the dependency section in your build.gradle:

testImplementation 'org.json:json:20180813'

Note that you also need to use Android Studio 1.1 or higher and at least build tools version 22.0.0 or above for this to work!

testImplementation means that the dependency is included as a test dependency will only be used when your project is being compiled for executing unit tests. The supplied jar will not be included in your APK and will only be used to replace the missing classes in the org.json package.