### Question:
StringSubstitutionEngine implements StringSubstitutor { @Override public void substituteComponents(List<String> components) throws StringSubstitutionException { if (!isValid(components)) { throw new StringSubstitutionException(STRINGS.get("missingComponentIdentifiers")); } for (String componentId : components) { Component component = findComponentById(componentId); if (component == null) { LOGGER.log(Level.INFO, SLogger.MISSING_COMPONENT, componentId); continue; } doSubstitution(component); } } StringSubstitutionEngine(InputStream inputStream); @Override void setAttributePreprocessor(AttributePreprocessor attributePreprocessor); @Override void setEntryFactory(SubstitutableFactory factory); @Override void setFileBackupLocation(File backupLocation); @Override List<Property> getDefaultProperties(PropertyType type); @Override void substituteAll(); @Override void substituteComponents(List<String> components); @Override void substituteGroups(List<String> groups); @Override StringsubsDefinition getStringSubsDefinition();  }### Answer:
@Test public void testSubstitutionForNullComponent() { try { _engine.substituteComponents(null); } catch (StringSubstitutionException e) { return; } Assert.fail("Allowing to peform substitution for null Component."); }
@Test public void testSubstitutionForEmptyComponent() { try { _engine.substituteComponents(new ArrayList<String>(1)); } catch (StringSubstitutionException e) { return; } Assert.fail("Allowing to peform substitution for empty Component."); }
@Test public void testSubstitutionForInvalidComponent() { List<String> componentIDs = new ArrayList<String>(1); componentIDs.add("invalidComponent"); try { _engine.substituteComponents(componentIDs); } catch (StringSubstitutionException e) { Assert.fail("Throwing exception if invalid Component id is passed for susbtitution."); return; } }
@Test public void testSubstitutionForComponentWithoutGroup() { List<String> componentIDs = new ArrayList<String>(1); componentIDs.add("component_without_group"); try { _engine.substituteComponents(componentIDs); } catch (StringSubstitutionException e) { Assert.fail("Throwing exception if invalid Component id is passed for susbtitution."); return; } }