使用Robolectric测试Android DecimalFormat

Question

The Android library modified the DecimalFormat class with some nice additions. Of course, I need one of those additions (the signifant digit notation: @ ).

When I'm testing with Robolectric, it seems that the standard Java DecimalFormat class is used, which makes my tests fail.

Is there a way to tell Robolectric to use the Android version? Or should I include DecimalFormat in my project (copy/pasting the class from AOSP?)?

Here's a stripped down example:

If I run the App on a device with the following:

import java.text.DecimalFormat;
import java.util.Locale;

public class App extends Application {
    @Override
    public void onCreate() {
        super.onCreate();
        DecimalFormat decimalFormat = (DecimalFormat)java.text.NumberFormat.getInstance(Locale.US);
        decimalFormat.applyPattern("@@@");
        Log.d('SO', decimalFormat.format(0.0567467));
    }
}

It displays:

W/App: 0.0567

In the Unit tests:

import org.junit.Test;
import org.junit.runner.RunWith;
import org.robolectric.RobolectricGradleTestRunner;
import org.robolectric.annotation.Config;
import java.text.DecimalFormat;
import java.util.Locale;

import static junit.framework.TestCase.assertEquals;


@RunWith(RobolectricGradleTestRunner.class)
@Config(constants = BuildConfig.class, sdk = 21)
public class NumberFormatTest {
    @Test
    public void testSignificantDigit() {
        DecimalFormat decimalFormat = (DecimalFormat)java.text.NumberFormat.getInstance(Locale.US);
        decimalFormat.applyPattern("@@@");
        assertEquals("0.0567", decimalFormat.format(0.0567467));
    }
}

Running the test will output:

junit.framework.ComparisonFailure:

Expected :0.0567

Actual :@@@0

Answer 1

As the official android documentation states, the implementation offered when running your java code in an Android RunTime (ART) differs from the one in a regular JVM.

RoboElectric does not run tests on a regular android phone or an emulator but on a JVM instead. This JVM, running on your host system, does not have this modified runtime implementation version of DecimalFormat. Therefore as far as I know the functionality Android offers is not available when running your test code in a JVM. To be able to use it, run your tests on an android phone, but then you may get rid of RoboElectric for that test anyway but use the offered testing tools .

Another logical question: Why do you want to test Android classes? I guess Google already wrote tests for there changes and keeps track of that, so you should no test functionality offered to you by the system you're using .