Bitmap.CreateBitmap return null in JUnit Testing Android Studio

Question

I need to create a fake bitmap image for testing (JUnit Test) my personal add and get methods of a custom LinkedList but the Bitmap.createBitmap return the error:

java.lang.RuntimeException: Method createBitmap in android.graphics.Bitmap not mocked.

This is the code of my JUnitTest:

public class TicketsIteratorTest {

    Bitmap img_Bmp;
    TicketsIterator<Bitmap> TicketsList = new TicketsIterator();

    /*
     * Test for the add e get methods, check if the element just insert it's the same of the one just extract.
     */
    @Test
    public void Add_n_Get() throws Exception {
        int i = 0, numIMG = 100;
        Bitmap[] IMG_Generated;
        IMG_Generated = new Bitmap[numIMG];

        // Generate numIMG of imagine to insert into the Iterator and it save each one of it into an
        // Bitmap array usefull for testing of the get method
        while (i <= numIMG) {
            // Generation of the fake Ticket Bitmap
            try {
                img_Bmp = Bitmap.createBitmap(100, 100, Bitmap.Config.ARGB_8888);

                IMG_Generated[i] = img_Bmp;

            } catch (Exception e) {
                // Print the cause of the error just generated
                e.getCause().printStackTrace();
            }

            // Addition of the imagine just created
            TicketsList.add(img_Bmp);

            i++;
        }

        // Test if the imagine inserted it is correct
        while (i <= numIMG) {
            assertTrue(IMG_Generated[i] == TicketsList.get(IMG_Generated[i]));
            i++;
        }
    }

Thank you for the help.

Answer 1

Are you using this in regular unit tests or in Android Tests? If you are calling this from normal unit test, android classes will be replaced with empty/null implementation. This means call to Bitmap.createBitmap() will just always return null without even checking yours parameters etc.

I had similar issue in the past with Bitmap and with Base64OutputStream. Everything seems to be working perfectly fine, except nothing is happening behind ;) Whenever you will see similar behaviour check if class is not from Android framework - that will be most probably the reason for problems.

I hope that was that and I could help you. I am using PowerMock and just mocked Bitmap class to return Bitmap mock instance in my case.

best regards,

Dariusz Wiechecki

Answer 2

Instrumentation Test case will work in this case, Unit test case will return null (fail) for bitmap because it's related to Android framework.

I faced similar type of issue while reading a file from connected device (Mobile) filepath in Unit test case, it couldn't read but it works in Instrumentation Test

Answer 3

You can use the kotlin extension toBitmap() from a drawable.

ContextCompat.getDrawable(context, R.drawable.x)?.toBitmap()