Invoice.java

package nl.tudelft.mocks;

public class Invoice {

    private String customer;
    private double value;

    public Invoice(String customer, double value) {
        this.customer = customer;
        this.value = value;
    }

    public String getCustomer() {
        return customer;
    }

    public double getValue() {
        return value;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        Invoice invoice = (Invoice) o;

        if (Double.compare(invoice.value, value) != 0) return false;
        return customer != null ? customer.equals(invoice.customer) : invoice.customer == null;
    }

    @Override
    public int hashCode() {
        int result;
        long temp;
        result = customer != null ? customer.hashCode() : 0;
        temp = Double.doubleToLongBits(value);
        result = 31 * result + (int) (temp ^ (temp >>> 32));
        return result;
    }
}

InvoiceDao.java

package nl.tudelft.mocks;

import java.sql.*;
import java.util.ArrayList;
import java.util.List;

public class InvoiceDao {

    private static final Connection c;

    static {
        try {
            c = DriverManager.getConnection("jdbc:hsqldb:mem:mymemdb", "SA", "");
            c.prepareStatement("create table invoice (name varchar(100), value double)").execute();
        } catch (SQLException e) {
            throw new RuntimeException(e);
        }
    }

    public List<Invoice> all() {

        List<Invoice> allInvoices = new ArrayList<>();

        try {
            PreparedStatement ps = c.prepareStatement("select * from invoice");

            ResultSet rs = ps.executeQuery();

            while(rs.next()) {
                String name = rs.getString("name");
                double value = rs.getDouble("value");
                allInvoices.add(new Invoice(name, value));
            }

        } catch (SQLException e) {
            throw new RuntimeException(e);
        } finally {
            return allInvoices;
        }

    }

    public void save(Invoice inv) {
        try {
            PreparedStatement ps = c.prepareStatement("insert into invoice (name, value) values (?,?)");
            ps.setString(1, inv.getCustomer());
            ps.setDouble(2, inv.getValue());

            ps.execute();

            c.commit();
        } catch (SQLException e) {
            throw new RuntimeException(e);
        }
    }
    
    public void close() {
        try {
            c.close();
        } catch (SQLException e) {
            throw new RuntimeException(e);
        }
    }
}

InvoiceFilter.java

package nl.tudelft.mocks;

import java.util.ArrayList;
import java.util.List;
import java.util.Queue;

public class InvoiceFilter {


    public List<Invoice> filter() {

        InvoiceDao invoiceDao = new InvoiceDao();
        List<Invoice> filtered = new ArrayList<>();

        List<Invoice> allInvoices = invoiceDao.all();

        for(Invoice inv : allInvoices) {
            if(inv.getValue() < 100.0)
                filtered.add(inv);
        }

        return filtered;

    }
}

InvoiceFilterTest.java

package nl.tudelft.mocks;


import static org.assertj.core.api.Assertions.assertThat;
import org.junit.jupiter.api.Test;

import java.util.List;

public class InvoiceFilterTest {


    @Test
    void filterInvoices() {

        InvoiceDao dao = new InvoiceDao();
        Invoice mauricio = new Invoice("Mauricio", 20.0);
        Invoice arie = new Invoice("Arie", 300.0);

        dao.save(mauricio);
        dao.save(arie);

        InvoiceFilter filter = new InvoiceFilter();
        List<Invoice> result = filter.filter();

        assertThat(result).containsExactly(mauricio);

        dao.close();
    }
}

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>nl.tudelft</groupId>
    <artifactId>mocks</artifactId>
    <version>1.0-SNAPSHOT</version>


    <dependencies>


        <!-- https://mvnrepository.com/artifact/org.hsqldb/hsqldb -->
        <dependency>
            <groupId>org.hsqldb</groupId>
            <artifactId>hsqldb</artifactId>
            <version>2.4.0</version>
        </dependency>


        <!-- https://mvnrepository.com/artifact/org.assertj/assertj-core -->
        <dependency>
            <groupId>org.assertj</groupId>
            <artifactId>assertj-core</artifactId>
            <version>3.7.0</version>
            <scope>test</scope>
        </dependency>

        <!-- https://mvnrepository.com/artifact/org.junit.jupiter/junit-jupiter-api -->
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-api</artifactId>
            <version>5.0.0-M4</version>
        </dependency>


        <!-- https://mvnrepository.com/artifact/org.mockito/mockito-core -->
        <dependency>
            <groupId>org.mockito</groupId>
            <artifactId>mockito-core</artifactId>
            <version>2.7.22</version>
            <scope>test</scope>
        </dependency>

    </dependencies>
</project>