canvas.drawText() produces empty bitmap

[obfusk]

Description

Drawing a letter on a canvas with .drawText() to produce a bitmap works as expected on Android devices but produces an empty bitmap during unit tests.

This issue seems similar to #7188.

Steps to Reproduce

See code below. Adding assertFalse(bitmap1.sameAs(bitmap2)) makes the test fail; even though the bitmaps should have different colours and letters they are both blank and identical.

Robolectric & Android Version

4.10.3 & N/A

Link to a public git repo demonstrating the problem:

Code that uses .drawText() on a canvas:

https://github.com/CatimaLoyalty/Android/blob/b9d9c8d/app/src/main/java/protect/card_locker/LetterBitmap.java#L93

Test that uses that code and produces an unexpectedly empty transparent bitmap (e.g. when exported via bitmap.compress(Bitmap.CompressFormat.PNG, 100, fileOutputStream):

https://github.com/CatimaLoyalty/Android/blob/b9d9c8d/app/src/test/java/protect/card_locker/ImportExportTest.java#L758

cc @TheLastProject