Integration Tests with Java

Integration Tests with Java

This document aims to give an overview how to do integration tests in Java with JUnit4. For all integration tests we want to use testcontainers so they can run isolated from each other with their own small docker container.

Testcontainers

see https://www.testcontainers.org/quickstart/junit_4_quickstart/ for a quickstart. For some usecases and/or container types there already are some containers and/or tutorials provided.

with PostgreSQL database

set up container

You can create a Postgresql container in each test with:

public void testMethod() throws IOException {
  try(PostgreSQLContainer postgres = newPostgreSQLContainer()) {
    postgres.start();
    [...]
  }
}

To establish a connection with JDBC the following snipped is needed:

public void initDatabaseStuff(PostgreSQLContainer container) {
  // JDBC driver name and database URL
  String db_url = container.getJdbcUrl();
  String user = container.getUsername();
  String password = container.getPassword();

  Connection conn = null;
  Statement stmt = null; // later used for sending queries
  try{
    // Register JDBC driver
    Class.forName("org.postgresql.Driver");

    // Open a connection
    System.out.println("Connecting to a database...");
    conn = DriverManager.getConnection(db_url, user, password);
    System.out.println("Connected database successfully...");

    }catch(Exception e){
      e.printStackTrace();
    }finally{
      //finally block used to close resources
      try{
        if(stmt!=null)
          conn.close();
      }catch(SQLException se){
      }// do nothing
      try{
          if(conn!=null)
            conn.close();
      }catch(SQLException se){
          se.printStackTrace();
      }//end finally try
    }//end try
    System.out.println("Goodbye!");
  }

Here we fetch the container's connection information and pass it to a JDBC connection.

To execute queries stmt.executeQuery("select * from tablename") suffices.

If you need to access query results, use something like ResultSet result = stmt.executeQuery("select * from tablename"). You can iterate over a ResultSet similar to an iterator with result.next():