Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.4.1)
// Compass (v1.0.1)
// ----

.foo {
  background: green;  
}

.bar {
  color: blue;
}

.foo.bar {
  border: 2px solid red;  
}

/*
 * We want the following:
 * 
 * .test {
 *   background: green;
 *   color: blue;
 *   border: 2px solid red;
 * }
 */

.test {
    @extend .foo;
    @extend .bar;
}

SassMeister-output.css

.foo, .test {
  background: green;
}

.bar, .test {
  color: blue;
}

.foo.bar, .test {
  border: 2px solid red;
}

/*
 * We want the following:
 * 
 * .test {
 *   background: green;
 *   color: blue;
 *   border: 2px solid red;
 * }
 */