diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..6f8aeee
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,4 @@
+doble_initial.exe
+highscores.txt
+runStackTest.exe
+stack.o
diff --git a/makefile b/makefile
index 1f15f75..5893c0b 100644
--- a/makefile
+++ b/makefile
@@ -1,49 +1,49 @@
-CC = gcc
-FLAGS = -g -Wall -lm
-
-ifeq ($(OS),Windows_NT)
-	include makefile_windows.variables
-else
-	UNAME = $(shell uname)
-	ifeq ($(UNAME),Linux)
-		include makefile_linux.variables
-	else
-		include makefile_mac.variables
-	endif
-endif
-
-raylibfolder = ./raylib
-unityfolder = ./unity
-
-# --------------------------
-# Initiales Programm bauen (zum ausprobieren)
-# --------------------------
-doble_initial:
-	$(CC) -o doble_initial $(BINARIES)/libdoble_complete.a
-
-# --------------------------
-# Selbst implementiertes Programm bauen
-# --------------------------
-program_obj_files = stack.o bintree.o numbers.o timer.o highscore.o
-
-doble : main.o $(program_obj_files)
-	$(CC) $(FLAGS) $^ -o doble
-
-$(program_obj_filesobj_files): %.o: %.c
-	$(CC) -c $(FLAGS) $^ -o $@
-
-# --------------------------
-# Unit Tests
-# --------------------------
-unitTests:
-	echo "needs to be implemented"
-
-# --------------------------
-# Clean
-# --------------------------
-clean:
-ifeq ($(OS),Windows_NT)
-	del /f *.o doble
-else
-	rm -f *.o doble
+CC = gcc
+FLAGS = -g -Wall -lm
+
+ifeq ($(OS),Windows_NT)
+	include makefile_windows.variables
+else
+	UNAME = $(shell uname)
+	ifeq ($(UNAME),Linux)
+		include makefile_linux.variables
+	else
+		include makefile_mac.variables
+	endif
+endif
+
+raylibfolder = ./raylib
+unityfolder = ./unity
+
+# --------------------------
+# Initiales Programm bauen (zum ausprobieren)
+# --------------------------
+doble_initial:
+	$(CC) -o doble_initial $(BINARIES)/libdoble_complete.a
+
+# --------------------------
+# Selbst implementiertes Programm bauen
+# --------------------------
+program_obj_files = stack.o bintree.o numbers.o timer.o highscore.o
+
+doble : main.o $(program_obj_files)
+	$(CC) $(FLAGS) $^ -o doble
+
+$(program_obj_filesobj_files): %.o: %.c
+	$(CC) -c $(FLAGS) $^ -o $@
+
+# --------------------------
+# Unit Tests
+# --------------------------
+unitTests: stack.o test_stack.c $(unityfolder)/unity.c
+	$(CC) $(FLAGS) -I$(unityfolder) -o runStackTest test_stack.c stack.o $(unityfolder)/unity.c
+
+# --------------------------
+# Clean
+# --------------------------
+clean:
+ifeq ($(OS),Windows_NT)
+	del /f *.o doble
+else
+	rm -f *.o doble
 endif
\ No newline at end of file
diff --git a/stack.c b/stack.c
index e3a90d4..5bfb882 100644
--- a/stack.c
+++ b/stack.c
@@ -1,33 +1,91 @@
-#include <stdlib.h>
-#include "stack.h"
-
-//TODO: grundlegende Stackfunktionen implementieren:
-/*  * `push`: legt ein Element oben auf den Stack,
-    * `pop`: entfernt das oberste Element,
-    * `top`: liefert das oberste Element zurück,
-    * `clearStack`: gibt den gesamten Speicher frei. */
-
-// Pushes data as pointer onto the stack.
-StackNode *push(StackNode *stack, void *data)
-{
-
-}
-
-// Deletes the top element of the stack (latest added element) and releases its memory. (Pointer to data has to be
-// freed by caller.)
-StackNode *pop(StackNode *stack)
-{
-
-}
-
-// Returns the data of the top element.
-void *top(StackNode *stack)
-{
-
-}
-
-// Clears stack and releases all memory.
-void clearStack(StackNode *stack)
-{
-
+#include <stdlib.h>
+#include "stack.h"
+
+// TODO: grundlegende Stackfunktionen implementieren:
+/*  * `push`: legt ein Element oben auf den Stack,
+ * `pop`: entfernt das oberste Element,
+ * `top`: liefert das oberste Element zurück,
+ * `clearStack`: gibt den gesamten Speicher frei. */
+
+// Pushes data as pointer onto the stack.
+StackNode *push(StackNode *stack, void *data)
+{
+    StackNode *tempNode, *newNode;
+
+    newNode = malloc(sizeof(StackNode));
+    newNode->value = 3;
+    newNode->next = NULL;
+
+    if (stack == NULL)
+    {
+        stack = newNode;
+        return stack;
+    }
+
+    tempNode = stack;
+    while (tempNode->next != NULL)
+    {
+        tempNode = tempNode->next;
+    }
+    tempNode->next = newNode;
+
+    return stack;
+}
+
+// Deletes the top element of the stack (latest added element) and releases its memory. (Pointer to data has to be
+// freed by caller.)
+StackNode *pop(StackNode *stack)
+{
+    StackNode *tempNode;
+
+    if (stack == NULL)
+    {
+        return stack;
+    }
+
+    tempNode = stack;
+    while (tempNode->next->next != NULL)
+    {
+        tempNode = tempNode->next;
+    }
+    free(tempNode->next);
+    tempNode->next = NULL;
+
+    return stack;
+}
+
+// Returns the data of the top element.
+void *top(StackNode *stack)
+{
+    StackNode *tempNode;
+
+    if (stack == NULL)
+    {
+        return NULL;
+    }
+
+    tempNode = stack;
+    while (tempNode->next != NULL)
+    {
+        tempNode = tempNode->next;
+    }
+
+    return &tempNode->value;
+}
+
+// Clears stack and releases all memory.
+void clearStack(StackNode *stack)
+{
+    StackNode *tempNode;
+
+    if (stack == NULL)
+    {
+        return;
+    }
+
+    tempNode = stack;
+    while (tempNode != NULL)
+    {
+        tempNode = pop(tempNode);
+    }
 }
\ No newline at end of file
diff --git a/stack.h b/stack.h
index f7d542d..d7cc86a 100644
--- a/stack.h
+++ b/stack.h
@@ -1,25 +1,29 @@
-#ifndef STACK_H
-#define STACK_H
-
-/* A stack is a special type of queue which uses the LIFO (last in, first out) principle. 
-This means that with each new element all other elements are pushed deeper into the stack. 
-The latest element is taken from the stack. */
-
-#include <stdlib.h>
-
-//TODO: passenden Datentyp als struct anlegen
-
-// Pushes data as pointer onto the stack.
-StackNode *push(StackNode *stack, void *data);
-
-// Deletes the top element of the stack (latest added element) and releases its memory. (Pointer to data has to be
-// freed by caller.)
-StackNode *pop(StackNode *stack);
-
-// Returns the data of the top element.
-void *top(StackNode *stack);
-
-// Clears stack and releases all memory.
-void clearStack(StackNode *stack);
-
-#endif
+#ifndef STACK_H
+#define STACK_H
+
+/* A stack is a special type of queue which uses the LIFO (last in, first out) principle. 
+This means that with each new element all other elements are pushed deeper into the stack. 
+The latest element is taken from the stack. */
+
+#include <stdlib.h>
+
+//TODO: passenden Datentyp als struct anlegen
+typedef struct Node {
+    int value;
+    struct Node* next;
+} StackNode;
+
+// Pushes data as pointer onto the stack.
+StackNode *push(StackNode *stack, void *data);
+
+// Deletes the top element of the stack (latest added element) and releases its memory. (Pointer to data has to be
+// freed by caller.)
+StackNode *pop(StackNode *stack);
+
+// Returns the data of the top element.
+void *top(StackNode *stack);
+
+// Clears stack and releases all memory.
+void clearStack(StackNode *stack);
+
+#endif
diff --git a/test_stack.c b/test_stack.c
new file mode 100644
index 0000000..2acb342
--- /dev/null
+++ b/test_stack.c
@@ -0,0 +1,89 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include "stack.h"
+#include "unity.h"
+
+StackNode* setup(int value, StackNode* next) {
+    StackNode* node = malloc(sizeof(StackNode)); // allocate memory on heap
+    if (node == NULL) {
+        perror("malloc failed");
+        exit(EXIT_FAILURE); // or handle the error differently
+    }
+    node->value = value;
+    node->next = next;
+    return node;
+}
+
+void test_pop(void)
+{   
+    StackNode* node2 = setup(3, NULL);
+    StackNode* node1 = setup(2, node2);
+    StackNode* header = setup(1, node1);
+    StackNode* temp;
+
+    temp = pop(header);
+    int after = 0;
+    while(temp) 
+    {
+        after++;
+        temp = temp->next;
+    }
+
+    
+    TEST_ASSERT_EQUAL_INT(2, after);
+    TEST_ASSERT_NULL(node1->next);
+}
+
+void test_top(void)
+{
+    StackNode* node2 = setup(3, NULL);
+    StackNode* node1 = setup(2, node2);
+    StackNode* header = setup(1, node1);
+
+    int data = *(int *)top(header);
+    TEST_ASSERT_EQUAL_INT(node2->value, data);
+}
+
+void test_clear()
+{
+    StackNode* node2 = setup(3, NULL);
+    StackNode* node1 = setup(2, node2);
+    StackNode* header = setup(1, node1);
+    StackNode* temp;
+    
+    clearStack(header);
+    temp = header;
+    
+    int after = 0;
+    while(temp) 
+    {
+        after++;
+        temp = temp->next;
+    }
+
+    
+    TEST_ASSERT_NULL(after);
+}
+
+void setUp(void)
+{
+    // Falls notwendig, kann hier Vorbereitungsarbeit gemacht werden
+}
+
+void tearDown(void)
+{
+    // Hier kann Bereinigungsarbeit nach jedem Test durchgeführt werden
+}
+
+int main()
+{
+    UNITY_BEGIN();
+
+    printf("============================\nStack tests\n============================\n");
+
+    RUN_TEST(test_pop);
+    RUN_TEST(test_top);
+    RUN_TEST(test_clear);
+
+    return UNITY_END();
+}
\ No newline at end of file
diff --git a/unittest.h b/unittest.h
new file mode 100644
index 0000000..ff5faa9
--- /dev/null
+++ b/unittest.h
@@ -0,0 +1,10 @@
+#ifndef UNITTTESTS_H
+#define UNITTTESTS_H
+
+#include <stdio.h>
+
+typedef int (*UnitTestType)(void);
+
+#define RUN_UNIT_TEST(fct) printf("%80s: %d\n", #fct, fct())
+
+#endif