### Question:
MutableTomlTable implements TomlTable { @Override @Nullable @SuppressWarnings("unchecked") public Object get(List<String> path) { if (path.isEmpty()) { return this; } Element element = getElement(path); return (element != null) ? element.value : null; } MutableTomlTable(); private  MutableTomlTable(boolean implicitlyDefined); @Override int size(); @Override boolean isEmpty(); @Override Set<String> keySet(); @Override Set<List<String>> keyPathSet(boolean includeTables); @Override @Nullable @SuppressWarnings("unchecked") Object get(List<String> path); @Override @Nullable TomlPosition inputPositionOf(List<String> path); @Override Map<String, Object> toMap();  }### Answer:
@Test void throwsForInvalidKey() { MutableTomlTable table = new MutableTomlTable(); IllegalArgumentException e = assertThrows(IllegalArgumentException.class, () -> { table.get("foo.=bar"); }); assertEquals("Invalid key: Unexpected '=', expected a-z, A-Z, 0-9, ', or \"", e.getMessage()); }