First two tests working

src/Life.java

 public class Life implements ILife {
-  
+
+  boolean[][] cells = new boolean[15][15];
+
   public static void main(String[] args) {
     Life l = new Life(new String[] {  "     ",
                                       "     ",
   @Override
   public void nukeAll() {
     // TODO Auto-generated method stub
-
+    for (int i = 0; i < 15; i++) {
+      for (int j = 0; j < 15; j++) {
+        cells[i][j] = false;
+      }
+    }
   }
 
   @Override
   public void setAlive(int x, int y) {
     // TODO Auto-generated method stub
-
+    cells[x][y] = true;
   }
 
   @Override
   public void setDead(int x, int y) {
     // TODO Auto-generated method stub
-
+    cells[x][y] = false;
   }
 
   @Override
   public boolean isAlive(int x, int y) {
     // TODO Auto-generated method stub
-    return false;
+    return cells[x][y];
   }
 
   @Override
   public ILife nextGeneration() {
     // TODO Auto-generated method stub
-    return null;
+    boolean[][] nextGen = new boolean[15][15];
+
+    for (int y = 0; y < 15; y++) {
+
+      for (int x = 0; x < 15; x++) {
+
+        int aliveNeighbours = countNeighbourCells(x, y);
+        if (isAlive(x, y)) {
+
+          if (aliveNeighbours == 2 || aliveNeighbours == 3) {
+            nextGen[x][y] = true;
+          } else {
+            nextGen[x][y] = false;
+          }
+        } else {
+          if (aliveNeighbours == 3) {
+            nextGen[x][y] = true;
+          } else {
+            nextGen[x][y] = false;
+          }
+        }
+      }
+    }
+    cells = nextGen;
+    return this;
+  }
+
+  public int countNeighbourCells(int x , int y){
+    int counter = 0;
+
+    if((x-1) >=0 && (y-1) >=0 && isAlive(x-1,y-1)) counter++;
+    if((y-1) >=0 && isAlive(x,y-1)) counter++;
+    if((x+1) < 15 && (y-1) >=0 && isAlive(x+1,y-1)) counter++;
+    if((x-1) >=0&& isAlive(x-1,y)) counter++;
+    if((x+1) < 15 && isAlive(x+1,y)) counter++;
+    if((x-1) >=0 && (y+1) < 15 && isAlive(x-1,y+1)) counter++;
+
+    if((y+1) <15 && isAlive(x,y+1)) counter++;
+
+    if((x+1) <15 && (y+1) <15 && isAlive(x+1,y+1)) counter++;
+
+    return counter;
   }
 }

test/LifeTest.java

 
     @Test
     public void destroyLonelyCell() {
+
+        // Arrange: drei lebende Zellen
+        Life l = new Life();
+        l.setAlive(0, 0);
+        l.setAlive(0, 1);
+
+        // Act: Berechnung der Folgegeneration
+        ILife nextGen = l.nextGeneration();
+
+        // Assert: Rasterpunkt mit drei Nachbarn sollte jetzt leben
+        assertTrue(!nextGen.isAlive(1, 1));
+
     }