### Question:
StringSubstitutionEngine implements StringSubstitutor { @Override public void substituteGroups(List<String> groups) throws StringSubstitutionException { if (!isValid(groups)) { throw new StringSubstitutionException(_strings.get("missingGroupIdentifiers")); } for (String groupId : groups) { Group group = findGroupById(groupId); if (group == null) { _logger.log(Level.WARNING, SLogger.MISSING_GROUP, groupId); continue; } doSubstitution(group); } } 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 testSubstitutionForNullGroup() { try { _engine.substituteGroups(null); } catch (StringSubstitutionException e) { return; } Assert.fail("Allowing to peform substitution for null Groups."); }
@Test public void testSubstitutionForEmptyGroup() { try { _engine.substituteGroups(new ArrayList<String>(1)); } catch (StringSubstitutionException e) { return; } Assert.fail("Allowing to peform substitution for empty Groups."); }
@Test public void testSubstitutionForInvalidGroup() { List<String> groupIDs = new ArrayList<String>(1); groupIDs.add("invalidGroup"); try { _engine.substituteGroups(groupIDs); } catch (StringSubstitutionException e) { Assert.fail("Throwing exception if invalid Group id is passed for susbtitution."); return; } }
@Test public void testSubstitutionForGroupWithoutChangePair() { List<String> groupIDs = new ArrayList<String>(1); groupIDs.add(GROUP_WITHOUT_CHANGE_PAIR); try { createTextFile(); _engine.substituteGroups(groupIDs); BufferedReader reader = null; try { reader = new BufferedReader(new InputStreamReader(new FileInputStream(_testFile))); String afterSubstitutionLine = null; int i = 0; while ((afterSubstitutionLine = reader.readLine()) != null) { switch (i++) { case 0: Assert.assertTrue(afterSubstitutionLine.equals("@ORACLE_HOME@ First word in first line")); break; case 1: Assert.assertTrue(afterSubstitutionLine.equals("Second line last word @MW_HOME@")); break; default: Assert.fail("Substitution happening for a Group without change pair."); break; } } } finally { if (reader != null) { reader.close(); } } } catch (Exception e) { Assert.fail("Throwing exception if Group without change pair undergo substitution."); return; } }
@Test public void testSubstitutionForGroupInvalidFilePath() { List<String> groupIDs = new ArrayList<String>(1); groupIDs.add(GROUP_WITH_INVALID_FILE_PATHS); try { _engine.substituteGroups(groupIDs); } catch (StringSubstitutionException e) { Assert.fail("Throwing exception if Group having invalid file paths undergo substitution."); return; } }
@Test public void testSubstitutionForGroupWithoutFiles() { List<String> groupIDs = new ArrayList<String>(1); groupIDs.add(GROUP_WITHOUT_FILES); try { _engine.substituteGroups(groupIDs); } catch (StringSubstitutionException e) { Assert.fail("Throwing exception if Group without any substitutable entries undergo substitution."); return; } }