diff --git a/src/TriangleChecker.java b/src/TriangleChecker.java
index c84987f..69f0b6d 100644
--- a/src/TriangleChecker.java
+++ b/src/TriangleChecker.java
@@ -47,11 +47,14 @@ public class TriangleChecker {
 
   // Analyse der Dreiecksart
   public static TriangleType checkTriangle(float a, float b, float c) {
+    if(a<=0 || b<=0 || c<=0 || a+b<c|| a+c<b || b+c<a){
+      return TriangleType.NONE;
+    }
     if(a==b && a==c){
       return TriangleType.EQUILATERAL;
       }
-    if(a<=0 || b<=0 || c<=0){
-      return TriangleType.NONE;
+    if(a==b || a==c || b==c){
+      return TriangleType.ISOSCELES;
     }
     else{
       return TriangleType.NORMAL;
diff --git a/test/TriangleCheckerTest.java b/test/TriangleCheckerTest.java
index 377b47e..e1bb969 100644
--- a/test/TriangleCheckerTest.java
+++ b/test/TriangleCheckerTest.java
@@ -80,4 +80,54 @@ public class TriangleCheckerTest {
         assertEquals(TriangleChecker.TriangleType.NONE, type);
 
     }
+
+    @Test
+    public void testValidNoTriangle4() {
+
+        // Arrange
+        float a = -1;
+        float b = -1;
+        float c = -1;
+
+        // Act
+        TriangleChecker.TriangleType type = TriangleChecker.checkTriangle(a, b, c);
+
+        // Assert
+        assertEquals(TriangleChecker.TriangleType.NONE, type);
+
+    }
+
+    @Test
+    public void testValidIsoscelesTriangle() {
+
+        // Arrange
+        float a = 3;
+        float b = 3;
+        float c = 4;
+
+        // Act
+        TriangleChecker.TriangleType type = TriangleChecker.checkTriangle(a, b, c);
+
+        // Assert
+        assertEquals(TriangleChecker.TriangleType.ISOSCELES, type);
+
+    }
+
+    @Test
+    public void testValidNoTriangle5() {
+
+        // Arrange
+        float a = 4;
+        float b = 4;
+        float c = 13;
+
+        // Act
+        TriangleChecker.TriangleType type = TriangleChecker.checkTriangle(a, b, c);
+
+        // Assert
+        assertEquals(TriangleChecker.TriangleType.NONE, type);
+
+    }
+
+
 }