test.java

package com.company;

import java.io.PrintWriter;
import java.sql.SQLException;

import static org.junit.Assert.assertEquals;

public class MainTest {

    @org.junit.Test
    public void testLogNormalError() {
        String stackTrace = "fake stack trace";
        Throwable e = new Throwable() {
            @Override
            public void printStackTrace(PrintWriter s) {
                s.print(stackTrace);
            }
        };
        assertEquals(stackTrace, Main.log(e));
    }

    @org.junit.Test
    public void testLogSqlError() {
        String stackTrace = "fake stack trace";
        int errorCode = 123456;
        Throwable e = new SQLException() {
            @Override
            public int getErrorCode() {
                return errorCode;
            }

            @Override
            public void printStackTrace(PrintWriter s) {
                s.print(stackTrace);
            }
        };
        assertEquals(
                "SQL exception error code: " + errorCode + stackTrace,
                Main.log(e)
        );
    }

}