Add unit test for GridItemDecoration

    public GridItemDecoration(@NonNull ItemAdapter adapter, int spanCount, @Px int sectionLeft, @Px int sectionTop, @Px int sectionRight, @Px int sectionBottom, @Px int gutter) {

        super(adapter, sectionLeft, sectionTop, sectionRight, sectionBottom);

        if(spanCount < 1) {

            throw new IllegalArgumentException("Requires at least one span");

        }

        this.spanCount = spanCount;

        this.adapter = adapter;

        this.gutter = gutter;

package it.niedermann.owncloud.notes.main.items.grid;

import android.graphics.Rect;

import android.os.Build;

import android.view.View;

import androidx.recyclerview.widget.RecyclerView;

import androidx.recyclerview.widget.StaggeredGridLayoutManager;

import org.junit.Test;

import org.junit.runner.RunWith;

import org.robolectric.RobolectricTestRunner;

import org.robolectric.annotation.Config;

import java.util.Arrays;

import it.niedermann.owncloud.notes.main.items.ItemAdapter;

import static org.junit.Assert.assertEquals;

import static org.junit.Assert.assertThrows;

import static org.mockito.ArgumentMatchers.any;

import static org.mockito.ArgumentMatchers.anyInt;

import static org.mockito.Mockito.mock;

import static org.mockito.Mockito.reset;

import static org.mockito.Mockito.verify;

import static org.mockito.Mockito.when;

@RunWith(RobolectricTestRunner.class)

@Config(sdk = {Build.VERSION_CODES.P})

public class GridItemDecorationTest {

    private final ItemAdapter itemAdapter = mock(ItemAdapter.class);

    private final RecyclerView recyclerView = mock(RecyclerView.class);

    private final View view = mock(View.class);

    private final StaggeredGridLayoutManager.LayoutParams layoutParams = mock(StaggeredGridLayoutManager.LayoutParams.class);

    @Test

    public void getItemOffsets() {

        when(view.getLayoutParams()).thenReturn(layoutParams);

        when(itemAdapter.getFirstPositionOfViewType(anyInt())).thenReturn(0);

        when(itemAdapter.getItemViewType(anyInt())).then((arg) -> Arrays.asList(0, 4, 9).contains(arg.getArgument(0, Integer.class))

                ? ItemAdapter.TYPE_SECTION

                : ItemAdapter.TYPE_NOTE_ONLY_TITLE);

        assertThrows("Requires at least one column", IllegalArgumentException.class, () -> new GridItemDecoration(itemAdapter, 0, 5, 5, 5, 5, 5));

        final GridItemDecoration oneColumn = new GridItemDecoration(itemAdapter, 1, 5, 5, 5, 5, 5);

        testAssertion(oneColumn, 0, 0, true, 5, 5, 5, 5);

        testAssertion(oneColumn, 0, 1, false, 0, 5, 5, 5);

        testAssertion(oneColumn, 0, 2, false, 0, 5, 5, 5);

        testAssertion(oneColumn, 0, 3, false, 0, 5, 5, 5);

        testAssertion(oneColumn, 0, 4, true, 5, 5, 5, 5);

        testAssertion(oneColumn, 0, 5, false, 0, 5, 5, 5);

        testAssertion(oneColumn, 0, 6, false, 0, 5, 5, 5);

        testAssertion(oneColumn, 0, 7, false, 0, 5, 5, 5);

        testAssertion(oneColumn, 0, 8, false, 0, 5, 5, 5);

        testAssertion(oneColumn, 0, 9, true, 5, 5, 5, 5);

        final GridItemDecoration twoColumns = new GridItemDecoration(itemAdapter, 2, 5, 5, 5, 5, 5);

        testAssertion(twoColumns, 0, 0, true, 5, 5, 5, 5);

        testAssertion(twoColumns, 0, 1, false, 0, 5, 5, 5);

        testAssertion(twoColumns, 1, 2, false, 0, 0, 5, 5);

        testAssertion(twoColumns, 0, 3, false, 0, 5, 5, 5);

        testAssertion(twoColumns, 0, 4, true, 5, 5, 5, 5);

        testAssertion(twoColumns, 0, 5, false, 0, 5, 5, 5);

        testAssertion(twoColumns, 1, 6, false, 0, 0, 5, 5);

        testAssertion(twoColumns, 0, 7, false, 0, 5, 5, 5);

        testAssertion(twoColumns, 0, 8, false, 0, 5, 5, 5);

        testAssertion(twoColumns, 0, 9, true, 5, 5, 5, 5);

        final GridItemDecoration threeColumns = new GridItemDecoration(itemAdapter, 3, 5, 5, 5, 5, 5);

        testAssertion(threeColumns, 0, 0, true, 5, 5, 5, 5);

        testAssertion(threeColumns, 0, 1, false, 0, 5, 5, 5);

        testAssertion(threeColumns, 1, 2, false, 0, 0, 5, 5);

        testAssertion(threeColumns, 2, 3, false, 0, 0, 5, 5);

        testAssertion(threeColumns, 0, 4, true, 5, 5, 5, 5);

        testAssertion(threeColumns, 0, 5, false, 0, 5, 5, 5);

        testAssertion(threeColumns, 1, 6, false, 0, 0, 5, 5);

        testAssertion(threeColumns, 2, 7, false, 0, 0, 5, 5);

        testAssertion(threeColumns, 0, 8, false, 0, 5, 5, 5);

        testAssertion(threeColumns, 0, 9, true, 5, 5, 5, 5);

    }

    @SuppressWarnings("SameParameterValue")

    private void testAssertion(GridItemDecoration gid, int spanIndex, int position, boolean fullSpan, int top, int left, int right, int bottom) {

        when(layoutParams.getSpanIndex()).thenReturn(spanIndex);

        when(recyclerView.getChildAdapterPosition(any())).thenReturn(position);

        final Rect result = new Rect();

        gid.getItemOffsets(result, view, recyclerView, mock(RecyclerView.State.class));

        if (fullSpan) {

            verify(layoutParams).setFullSpan(true);

        }

        reset(layoutParams);

        assertEquals(top, result.top);

        assertEquals(left, result.left);

        assertEquals(right, result.right);

        assertEquals(bottom, result.bottom);

    }

}

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