Testing The Impossible: Inserting Into Database

Tests run slow when you need a database. An in-memory database like HSQLDB or Derby helps but at a cost: Your real database will accept some SQL which your test database won’t. So the question is: How can you write a performant test which uses the SQL of the real database?

My solution is to wrap the JDBC layer. Either use a mock JDBC interface like the one provided by mockrunner. Or write your own. With Java 5 and varargs, this is simple:

public int update (Connection conn, String sql, Object... params) throws SQLException {
    PreparedStatement stmt = null;
    try {
        stmt = conn.prepareStatement (sql);
        int i = 1;
        for (Object p: params) {
            stmt.setObject(i++, p);
        return stmt.executeUpdate ();
    finally {
        stmt.close ();

Put all these methods into an object that you can pass around. In your tests, override this object with a mockup that simply collects the SQL strings and parameter arrays. You can even mix and match: By examining the SQL string, you can decide whether you want to run a query against the database or handle it internally.

This way, you can collect any newly created objects but still load some background data from the database (until you get bored and make the query methods return predefined results).

In the asserts, just collect all the results into a big String and compare them all at once.

Notes: The code above is a bit more complicated if you allow null values. In this case, you need to tell JDBC what the column type is. My solution is a NullParameter class which contains the type. If the loop encounters this class, then it calls setNull() instead of setObject().

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