### Question:
QueryTemplateServiceImpl implements QueryTemplateService { String replaceVariables(String queryGenerator, Map<String, VariableData> variables) { String newQuery = queryGenerator; Set<String> variableNames = variables.keySet(); for (String variableName : variableNames) { VariableData variable = variables.get(variableName); String newValue = variable.getStringValue(); newQuery = newQuery.replace("@" + variableName, newValue); } return newQuery; }  @Override PlatformQuery getTranslatedQuery(String ontology, String query); @Override List<QueryTemplate> getAllQueryTemplates(); @Override QueryTemplate createQueryTemplate(QueryTemplate queryTemplate); @Override boolean queryTemplateExists(QueryTemplate queryTemplate); @Override QueryTemplate getQueryTemplateById(String id); @Override List<QueryTemplate> getQueryTemplateByCriteria(String name); @Override void updateQueryTemplate(QueryTemplate queryTemplate);  }### Answer:
@Test public void given_AQueryTemplateAndASetOfVariables_When_TheVariablesAreReplaced_Then_AValidQueryTemplateIsGenerated() { String query = "var pipeline = [];\n" + "\n" + "pipeline.push(\n" + " {\n" + " $match: {\n" + " \"Test1.temperature.timestamp\": {\"$gte\" : ISODate(\"@var_from\"), \"$lt\" : ISODate(\"@var_to\") }\n" + " }\n" + " }\n" + ");\n" + "db.getCollection(\"AssetTestArray2\").aggregate(pipeline);\n" + "return \"db.AssetTestArray2.aggregate(\" + JSON.stringify(pipeline) + \")\";\n" + ""; String newQuery = "var pipeline = [];\n" + "\n" + "pipeline.push(\n" + " {\n" + " $match: {\n" + " \"Test1.temperature.timestamp\": {\"$gte\" : ISODate(\"2017-01-01T00:00:00.000Z\"), \"$lt\" : ISODate(\"2017-01-02T00:00:00.000Z\") }\n" + " }\n" + " }\n" + ");\n" + "db.getCollection(\"AssetTestArray2\").aggregate(pipeline);\n" + "return \"db.AssetTestArray2.aggregate(\" + JSON.stringify(pipeline) + \")\";\n" + ""; Map<String, VariableData> variables = new HashMap<>(); variables.put("var_from", new VariableData("var-from", VariableData.Type.STRING, "2017-01-01T00:00:00.000Z")); variables.put("var_to", new VariableData("var-to", VariableData.Type.STRING, "2017-01-02T00:00:00.000Z")); String resultQuery = service.replaceVariables(query, variables); assertTrue("The result query should have all the variables replaced", resultQuery.equals(newQuery)); }