src/main/java/view/WaitingMouseListener.java

 package view;
 
-import datastruct.Coordinate;
+import matrix.Coordinate;
 import javafx.scene.input.MouseEvent;
 
 class WaitingMouseListener implements MouseListener {

src/test/java/datastruct/ConstantMatrixInitializerTest.java → src/test/java/matrix/ConstantMatrixInitializerTest.java

-package datastruct;
+package matrix;
 
 import org.junit.jupiter.api.Test;
 
@@ -7,7 +7,7 @@ import static org.junit.jupiter.api.Assertions.*;
 class ConstantMatrixInitializerTest {
     @Test
     public void testMatrixInitializationWithConstantValue() {
-        Matrix<String> matrix = new Matrix<>(3, 3, new ConstantMatrixInitializer<>("X"));
+        ListMatrix<String> matrix = new ListMatrix<>(3, 3, new ConstantMatrixInitializer<>("X"));
 
         // Test that all cells have the constant value.
         for (int x = 0; x < 3; x++) {
@@ -19,7 +19,7 @@ class ConstantMatrixInitializerTest {
 
     @Test
     public void testMatrixInitializationWithConstantValue2() {
-        Matrix<Integer> matrix = new Matrix<>(3, 5, new ConstantMatrixInitializer<>(12));
+        ListMatrix<Integer> matrix = new ListMatrix<>(3, 5, new ConstantMatrixInitializer<>(12));
 
         // Test that all cells have the constant value.
         for (int x = 0; x < 3; x++) {

src/test/java/datastruct/CoordinateIteratorTest.java → src/test/java/matrix/CoordinateIteratorTest.java

-package datastruct;
+package matrix;
 
 import org.junit.jupiter.api.Test;
 

src/test/java/datastruct/CoordinateTest.java → src/test/java/matrix/CoordinateTest.java

-package datastruct;
+package matrix;
 
 import org.junit.jupiter.api.Test;
 

src/test/java/datastruct/MatrixTest.java → src/test/java/matrix/ListMatrixTest.java

-package datastruct;
+package matrix;
 
 import org.junit.jupiter.api.Test;
 
@@ -6,14 +6,14 @@ import java.util.Iterator;
 
 import static org.junit.jupiter.api.Assertions.*;
 
-class MatrixTest {
+class ListMatrixTest {
 
     private final MatrixInitializer<Integer> sumInitializer =
             coord -> coord.x() + coord.y();
 
     @Test
     public void testMatrixCreationWithInitializer() {
-        Matrix<Integer> matrix = new Matrix<>(3, 4, sumInitializer);
+        ListMatrix<Integer> matrix = new ListMatrix<>(3, 4, sumInitializer);
         assertEquals(3, matrix.width());
         assertEquals(4, matrix.height());
         assertEquals(4, matrix.get(2, 2));
@@ -24,7 +24,7 @@ class MatrixTest {
 
     @Test
     public void testMatrixCreationWithInitialValue() {
-        Matrix<String> matrix = new Matrix<>(2, 2, "Foo");
+        ListMatrix<String> matrix = new ListMatrix<>(2, 2, "Foo");
         assertEquals(2, matrix.width());
         assertEquals(2, matrix.height());
         assertEquals("Foo", matrix.get(1, 1)); // Test a specific cell value.
@@ -32,7 +32,7 @@ class MatrixTest {
 
     @Test
     public void testMatrixSetAndGet() {
-        Matrix<Integer> matrix = new Matrix<>(3, 3, 0);
+        ListMatrix<Integer> matrix = new ListMatrix<>(3, 3, 0);
         matrix.set(1, 1,42);
         assertEquals(42, matrix.get(1, 1));
         matrix.set(0, 2,10);
@@ -43,7 +43,7 @@ class MatrixTest {
 
     @Test
     public void testMatrixWidthAndHeight() {
-        Matrix<String> matrix = new Matrix<>(4, 2, "A");
+        ListMatrix<String> matrix = new ListMatrix<>(4, 2, "A");
         assertEquals(4, matrix.width());
         assertEquals(2, matrix.height());
         matrix.set(3, 1,"B");
@@ -53,7 +53,7 @@ class MatrixTest {
 
     @Test
     public void testMatrixIterator() {
-        Matrix<Integer> matrix = new Matrix<>(2, 2, sumInitializer);
+        ListMatrix<Integer> matrix = new ListMatrix<>(2, 2, sumInitializer);
         Iterator<Integer> iterator = matrix.iterator();
         assertTrue(iterator.hasNext());
         assertEquals(0, iterator.next());
@@ -68,7 +68,7 @@ class MatrixTest {
 
     @Test
     public void testMatrixCoordinates() {
-        Matrix<Integer> matrix = new Matrix<>(2, 2, 0);
+        ListMatrix<Integer> matrix = new ListMatrix<>(2, 2, 0);
         Iterable<Coordinate> coordinates = matrix.coordinates();
         int count = 0;
         for (Coordinate coord : coordinates) {
@@ -77,12 +77,24 @@ class MatrixTest {
         assertEquals(4, count);
     }
 
+
     @Test
-    public void testMatrixLens() {
-        Matrix<Integer> matrix = new Matrix<>(2, 2, 0);
-        Lens<Integer> lens = matrix.at(1, 1);
-        assertEquals(0, lens.get());
-        lens.set(42);
-        assertEquals(42, matrix.get(1, 1));
+    public void testSubMatrix() {
+      Matrix<Integer> matrix = new ListMatrix<>(5, 5, 0);
+      for (int x = 0; x < 5; x++) {
+        for (int y = 0; y < 5; y++) {
+          matrix.set(x,y,x + y * 5);
+        }
+      }
+      Matrix<Integer> sub = matrix.subMatrix(Coordinate.of(2,1),2,3);
+      assertEquals(2, sub.width());
+      assertEquals(3, sub.height());
+      for (int x = 2; x < 4; x++) {
+        for (int y = 1; y < 4; y++) {
+          assertEquals(x + y * 5, sub.get(x-2,y-1));
         }
       }
+    }
+
+
+}

src/test/java/model/CellularAutomatonSimulationTest.java

 package model;
 
-import datastruct.Coordinate;
+import matrix.Coordinate;
 import javafx.scene.paint.Color;
 import model.automata.GameOfLifeAutomaton;
 import static model.automata.GameOfLifeState.*;

src/test/java/model/NextGenerationInitializerTest.java

 package model;
 
-import controller.Simulation;
-import datastruct.Coordinate;
+import matrix.Coordinate;
 import model.automata.GameOfLifeAutomaton;
 import model.automata.GameOfLifeState;
 import org.junit.jupiter.api.BeforeEach;