### Question:
SnippetCompletion implements Completion { @Nonnull @Override public Collection<String> getCompletionSource(MyDocumentModel document) { return snippets.getLabels(); } @Inject  SnippetCompletion(@Named("Snippets") CompletionStorage snippets); @Nonnull @Override Collection<String> getCompletionSource(MyDocumentModel document); @Nullable @Override String tryResolve(@Nonnull String label); @Nonnull @Override String getSortOrderPrefix(); @Nonnull @Override CompletionItem customize(@Nonnull CompletionItem item); @Nonnull @Override CompletionItemKind getKind();  }### Answer:
@Test void testGetCompletionSource() { Collection<String> strings = provider.getCompletionSource(null); assertFalse(strings.isEmpty()); assertTrue(strings.contains(LABEL)); }