### Question:
TSNameSpace { public TSNameSpace getSubNameSapce(String thatName) { if (!this.children.containsKey(thatName)) throw new IllegalArgumentException("no namespace " + thatName + " in current node " + this.name); else return this.children.get(thatName); } private  TSNameSpace(String name, List<TSType> types, Map<String, TSNameSpace> children);  TSNameSpace(); private  TSNameSpace(String name); TSNameSpace findOrCreate(String namespace); void addType(TSType type); @Override String toString(); boolean isRoot(); String getName(); List<TSType> getTypes(); Set<String> getSubNamespaces(); TSNameSpace getSubNameSapce(String thatName);  }### Answer:
@Test @DisplayName("Check failing empty namespace") void testIllegalSubnameSpace() { assertThrows(IllegalArgumentException.class, () -> { TSNameSpace testee = new TSNameSpace(); testee.getSubNameSapce(""); } ); }