Optimize uploads during media composition.

By uploading in advance (when on unmetered connections), media messages
can send almost instantly.

app/src/test/java/org/thoughtcrime/securesms/util/DiffHelperTest.java

@@ -0,0 +1,57 @@
+package org.thoughtcrime.securesms.util;
+
+import androidx.annotation.NonNull;
+
+import org.junit.Test;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+public class DiffHelperTest {
+
+  private static final Object A = new Object();
+  private static final Object B = new Object();
+  private static final Object C = new Object();
+  private static final Object D = new Object();
+
+  @Test
+  public void calculate_allRemoved() {
+    DiffHelper.Result result = DiffHelper.calculate(Arrays.asList(A, B), Collections.emptyList());
+
+    assertContentsEqual(Collections.emptyList(), result.getInserted());
+    assertContentsEqual(Arrays.asList(A, B), result.getRemoved());
+  }
+
+  @Test
+  public void calculate_allInserted() {
+    DiffHelper.Result result = DiffHelper.calculate(Collections.emptyList(), Arrays.asList(A, B));
+
+    assertContentsEqual(Arrays.asList(A, B), result.getInserted());
+    assertContentsEqual(Collections.emptyList(), result.getRemoved());
+  }
+
+  @Test
+  public void calculate_completeSwap() {
+    DiffHelper.Result result = DiffHelper.calculate(Collections.singleton(A), Collections.singleton(B));
+
+    assertContentsEqual(Collections.singleton(B), result.getInserted());
+    assertContentsEqual(Collections.singleton(A), result.getRemoved());
+  }
+
+  @Test
+  public void calculate_bothEmpty() {
+    DiffHelper.Result result = DiffHelper.calculate(Collections.emptyList(), Collections.emptyList());
+
+    assertContentsEqual(Collections.emptyList(), result.getInserted());
+    assertContentsEqual(Collections.emptyList(), result.getRemoved());
+  }
+
+  private void assertContentsEqual(@NonNull Collection expected, @NonNull Collection actual) {
+    assertEquals(expected.size(), actual.size());
+    assertTrue(expected.containsAll(actual));
+  }
+}