Android: How to obtain Resources in non Activity test class?

Question

I have a class, Foo , that I am trying to write a test for, which the Foo constructor takes in a Resources object, which will then read some files from the Resources object.

The issue is, since both my class and test classes are NOT Activity classes, I do not see a good way of fetching a valid Resources object.

I have tried doing the following (yes I know these are NOT the proper way of achieving this at all):

Resources(null, null, null) // not null, but does not contain my R.raw.* files 
Resources.getSystem() // returns null
MainActivity().resources // returns null because onCreate is never called

my Kotlin test class is basic and looks like this

class FooTest {
    private val foo = Foo(Resources(null, null, null))
}

and my Java class looks like

public Foo(Resources resources) {

    InputStream is = resources.openRawResource(R.raw.stuff);
    Writer writer = new StringWriter();
    try {
        BufferedReader reader = new BufferedReader(new InputStreamReader(is, "UTF-8"));
        String line = reader.readLine();
        while (line != null) {
            writer.write(line);
            line = reader.readLine();
        }
    } catch (Exception e) {
        Log.e("ERROR", "Unhandled exception while using JSONResourceReader", e);
    } finally {
        try {
            is.close();
        } catch (Exception e) {
            Log.e("ERROR", "Unhandled exception while using JSONResourceReader", e);
        }
    }
    ...
}

How can I load the files from my resources properly?

Answer 1

Based off of the link from @IR42

in the end I had to include this in my testOptions unitTests.includeAndroidResources = true

these three dependencies

testImplementation('androidx.test:core:1.3.0')
testImplementation 'androidx.test.ext:junit-ktx:1.1.2'
testImplementation 'org.robolectric:robolectric:4.4'

and the following

@RunWith(AndroidJUnit4::class)
class FooTest {

    val context = ApplicationProvider.getApplicationContext<Context>()
    private val foo = Foo(context.resources)
}