made Methods public and added test file

Softwareengeneering.iml

     <exclude-output />
     <content url="file://$MODULE_DIR$">
       <sourceFolder url="file://$MODULE_DIR$/src" isTestSource="false" />
+      <sourceFolder url="file://$MODULE_DIR$/test" isTestSource="true" />
     </content>
     <orderEntry type="inheritedJdk" />
     <orderEntry type="sourceFolder" forTests="false" />
+    <orderEntry type="library" name="junit.jupiter" level="project" />
   </component>
 </module>

src/Praktikum01/Zahlenfilter.java

             }
         }
     }
-    public boolean filter(int i){
-        return !(checkDivideByFive(i) || checkEndsWithNine(i) || checkSumWithPrev(i)) ;
+    public static boolean filter(int i){
+        return !(checkDivideBy5(i) || checkEndsWith9(i) || checkSumDivideBy3(i)) ;
     }
     
-    private Boolean checkDivideByFive(int i) {
+    public static Boolean checkDivideBy5(int i) {
         return i % 5 == 0;
     }
 
 
-    private Boolean checkEndsWithNine(int i) {
+    public static Boolean checkEndsWith9(int i) {
         return i % 10 == 9;
     }
 
 
-    private Boolean checkSumWithPrev(int i) {
+    public static Boolean checkSumDivideBy3(int i) {
         if (i > 1) {
             int vorgaenger = i - 1;
             int summe = i + vorgaenger;

test/Praktikum01/ZahlenfilterTest.java

+package Praktikum01;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+class ZahlenfilterTest {
+
+    @Test
+    void filter() {
+    }
+
+    @Test
+    void checkDivideBy5() {
+        assertTrue( Zahlenfilter.checkDivideBy5(155));
+        assertFalse( Zahlenfilter.checkDivideBy5(0));
+        assertFalse( Zahlenfilter.checkDivideBy5(-3));
+    }
+
+    @Test
+    void checkEndsWith9() {
+        assertFalse( Zahlenfilter.checkEndsWith9(155));
+        assertFalse( Zahlenfilter.checkEndsWith9(0));
+        assertFalse( Zahlenfilter.checkEndsWith9(-3));
+        assertTrue(Zahlenfilter.checkEndsWith9(99));
+    }
+
+    @Test
+    void checkSumDivideBy3() {
+        assertTrue( Zahlenfilter.checkSumDivideBy3(155));
+    }
+}