Support DB2 functions in H2 database while unit testing

Question

We have a DB2 database in production, and we are setting up a H2 in-memory database for tests. I understand that not all DB2 functions are supported in H2 even when we configured it in DB2 mode. How do we unit test SQLs that contains database specific functions but are not yet supported in H2?

If we start writing H2 specific DB services then we will end writing different layer of functional code.

Function not supported

VARCHAR_FORMAT

H2 configuration

jdbc:h2:mem:test;MODE=DB2

H2 version

1.4.188

Java stacktrace

Caused by: org.h2.jdbc.JdbcSQLException: Function "VARCHAR_FORMAT" not found; SQL statement:
select S.SCHEDULE_ID scheduleId, VARCHAR_FORMAT(S.START_DATE, 'DD-Mon-YYYY') startDate
from ScheduleSubscription S WITH UR  [90022-182]
    at org.h2.message.DbException.getJdbcSQLException(DbException.java:345) ~[h2-1.4.182.jar:1.4.182]
    at org.h2.message.DbException.get(DbException.java:179) ~[h2-1.4.182.jar:1.4.182]
    at org.h2.message.DbException.get(DbException.java:155) ~[h2-1.4.182.jar:1.4.182]
    at org.h2.command.Parser.readJavaFunction(Parser.java:2333) ~[h2-1.4.182.jar:1.4.182]
    at org.h2.command.Parser.readFunction(Parser.java:2385) ~[h2-1.4.182.jar:1.4.182]
    at org.h2.command.Parser.readTerm(Parser.java:2719) ~[h2-1.4.182.jar:1.4.182]
    at org.h2.command.Parser.readFactor(Parser.java:2251) ~[h2-1.4.182.jar:1.4.182]
    at org.h2.command.Parser.readSum(Parser.java:2238) ~[h2-1.4.182.jar:1.4.182]
    at org.h2.command.Parser.readConcat(Parser.java:2208) ~[h2-1.4.182.jar:1.4.182]
    at org.h2.command.Parser.readCondition(Parser.java:2058) ~[h2-1.4.182.jar:1.4.182]
    at org.h2.command.Parser.readAnd(Parser.java:2030) ~[h2-1.4.182.jar:1.4.182]
    at org.h2.command.Parser.readExpression(Parser.java:2022) ~[h2-1.4.182.jar:1.4.182]
    at org.h2.command.Parser.parseSelectSimpleSelectPart(Parser.java:1934) ~[h2-1.4.182.jar:1.4.182]
    at org.h2.command.Parser.parseSelectSimple(Parser.java:1966) ~[h2-1.4.182.jar:1.4.182]
    at org.h2.command.Parser.parseSelectSub(Parser.java:1860) ~[h2-1.4.182.jar:1.4.182]
    at org.h2.command.Parser.parseSelectUnion(Parser.java:1681) ~[h2-1.4.182.jar:1.4.182]
    at org.h2.command.Parser.parseSelect(Parser.java:1669) ~[h2-1.4.182.jar:1.4.182]
    at org.h2.command.Parser.parsePrepared(Parser.java:433) ~[h2-1.4.182.jar:1.4.182]
    at org.h2.command.Parser.parse(Parser.java:305) ~[h2-1.4.182.jar:1.4.182]
    at org.h2.command.Parser.parse(Parser.java:277) ~[h2-1.4.182.jar:1.4.182]
    at org.h2.command.Parser.prepareCommand(Parser.java:242) ~[h2-1.4.182.jar:1.4.182]
    at org.h2.engine.Session.prepareLocal(Session.java:446) ~[h2-1.4.182.jar:1.4.182]
    at org.h2.engine.Session.prepareCommand(Session.java:388) ~[h2-1.4.182.jar:1.4.182]
    at org.h2.jdbc.JdbcConnection.prepareCommand(JdbcConnection.java:1190) ~[h2-1.4.182.jar:1.4.182]
    at org.h2.jdbc.JdbcPreparedStatement.<init>(JdbcPreparedStatement.java:72) ~[h2-1.4.182.jar:1.4.182]
    at org.h2.jdbc.JdbcConnection.prepareStatement(JdbcConnection.java:666) ~[h2-1.4.182.jar:1.4.182]
    at org.apache.commons.dbcp.DelegatingConnection.prepareStatement(DelegatingConnection.java:295) ~[commons-dbcp-1.4.jar:1.4]
    at org.apache.commons.dbcp.PoolingDataSource$PoolGuardConnectionWrapper.prepareStatement(PoolingDataSource.java:318) ~[commons-dbcp-1.4.jar:1.4]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.6.0_35]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) ~[na:1.6.0_35]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) ~[na:1.6.0_35]
    at java.lang.reflect.Method.invoke(Method.java:597) ~[na:1.6.0_35]
    at org.apache.ibatis.logging.jdbc.ConnectionLogger.invoke(ConnectionLogger.java:54) ~[mybatis-3.2.8.jar:3.2.8]
    at $Proxy35.prepareStatement(Unknown Source) ~[na:na]
    at org.apache.ibatis.executor.statement.PreparedStatementHandler.instantiateStatement(PreparedStatementHandler.java:73) ~[mybatis-3.2.8.jar:3.2.8]
    at org.apache.ibatis.executor.statement.BaseStatementHandler.prepare(BaseStatementHandler.java:85) ~[mybatis-3.2.8.jar:3.2.8]
    at org.apache.ibatis.executor.statement.RoutingStatementHandler.prepare(RoutingStatementHandler.java:57) ~[mybatis-3.2.8.jar:3.2.8]
    at org.apache.ibatis.executor.SimpleExecutor.prepareStatement(SimpleExecutor.java:73) ~[mybatis-3.2.8.jar:3.2.8]
    at org.apache.ibatis.executor.SimpleExecutor.doQuery(SimpleExecutor.java:59) ~[mybatis-3.2.8.jar:3.2.8]
    at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:267) ~[mybatis-3.2.8.jar:3.2.8]
    at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:137) ~[mybatis-3.2.8.jar:3.2.8]
    at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:96) ~[mybatis-3.2.8.jar:3.2.8]
    at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:77) ~[mybatis-3.2.8.jar:3.2.8]
    at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:108) ~[mybatis-3.2.8.jar:3.2.8]
    at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:102) ~[mybatis-3.2.8.jar:3.2.8]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.6.0_35]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) ~[na:1.6.0_35]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) ~[na:1.6.0_35]
    at java.lang.reflect.Method.invoke(Method.java:597) ~[na:1.6.0_35]
    at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:358) ~[mybatis-spring-1.2.2.jar:1.2.2]
    ... 47 common frames omitted

Answer 1

Create a H2 function called VARCHAR_FORMAT and make sure it returns proper values at least for the test data.

This of course requires effort for every function that doesn't already exist in H2, but is quite feasible. Tests stay clean too.