diff --git a/makefile b/makefile
index b792156..7bfefea 100644
--- a/makefile
+++ b/makefile
@@ -1,4 +1,4 @@
-```CC = gcc
+CC = gcc
 FLAGS = -g -Wall -lm
 
 ifeq ($(OS),Windows_NT)
diff --git a/stack.c b/stack.c
index 4fabf41..d0105c7 100644
--- a/stack.c
+++ b/stack.c
@@ -10,7 +10,7 @@
 // Pushes data as pointer onto the stack.
 StackNode *push(StackNode *stack, void *data) // es gibt bereits ein stack element, dieses wird übergeben + die daten, die in den stack müssen
 {
-    if(!stack || !data)
+    if(!data)
         return 0;
         
     StackNode *newNode = calloc(1, sizeof(StackNode)); //Speicher reserviert für data und prev, jeweils nur zeiger
diff --git a/stack.o b/stack.o
new file mode 100644
index 0000000..07999df
Binary files /dev/null and b/stack.o differ
diff --git a/test_runner b/test_runner
new file mode 100755
index 0000000..6bd81fe
Binary files /dev/null and b/test_runner differ
diff --git a/test_stack.c b/test_stack.c
index aaa0bd6..5ebf42f 100644
--- a/test_stack.c
+++ b/test_stack.c
@@ -9,9 +9,9 @@ void test_pushFailsOnNullPointer(StackNode *stack, void *data) {
     if (test != 0) {
         printf("Pass test_pushFailsOnNullPointerStack\n");
     } else 
-        printf("Did Not Pass test_pushFailsOnNullPointerStack EXPECTED Stac Node\n");
+        printf("Did Not Pass test_pushFailsOnNullPointerStack EXPECTED StackNode\n");
   
-    StackNode* test = push(stack, NULL);
+    test = push(stack, NULL);
     if (test == 0) {
         printf("Pass test_pushFailsOnNullPointerData\n");
         return;
@@ -24,35 +24,35 @@ void test_popFailsOnNullPointer() {
     
     StackNode* test = pop(NULL);
     if (test == 0) {
-        printf("Pass test_pushFailsOnNullPointerStack\n");
+        printf("Pass test_popFailsOnNullPointerStack\n");
         return;
     }
-    printf("Did Not Pass test_pushFailsOnNullPointerStack EXPECTED 0\n");
+    printf("Did Not Pass test_popFailsOnNullPointerStack EXPECTED 0\n");
     
     return;
 }
 
 void test_topFailsOnNullPointer() {
     
-    int* test = top(NULL);
+    int* test = (int*)top(NULL);
     if (test == 0) {
-        printf("Pass test_pushFailsOnNullPointerStack\n");
+        printf("Pass test_topFailsOnNullPointerStack\n");
         return;
     }
-    printf("Did Not Pass test_pushFailsOnNullPointerStack EXPECTED 0\n");
+    printf("Did Not Pass test_topFailsOnNullPointerStack EXPECTED 0\n");
     
     return;
 }
 
 int main()
 {
-    StackNode *stack0 = NULL;
+    
     int test0 = 3;
     int* dataTest0 = &test0;
-    stack0->data = dataTest0;
+    StackNode *stack0 = push(NULL, dataTest0);
 
     char test1[5] = "test\0";
-    char* dataTest1 = &test1;
+    char* dataTest1 = test1;
 
     float test2 = 3.14;
     float* dataTest2 = &test2;
@@ -72,7 +72,7 @@ int main()
     if(stack2->data == dataTest2) {
         printf("Pass test_pushFloat\n");
     } else
-        printf("Fails test_pushFloat\n expected: %f\n was: %d\n", dataTest2, stack2->data);
+        printf("Fails test_pushFloat\n expected: %f\n was: %f\n", dataTest2, *(float*)(stack2->data));
 
     int array[10] = {1,2,3,4,5,6,7,8,9,10};
 
@@ -80,8 +80,8 @@ int main()
         stack2 = push(stack2, &array[i]);
     }
     for(size_t i = 0; i<10; i++) {
-        int* data = top(stack2);
-        printf("%d\n", data);
+        int* data = (int*)top(stack2);
+        printf("%d\n", *data);
         stack2 = pop(stack2);
     }
 
diff --git a/unittest.o b/unittest.o
new file mode 100644
index 0000000..5f18b3b
Binary files /dev/null and b/unittest.o differ
diff --git a/unittest_stack.c b/unittest_stack.c
new file mode 100644
index 0000000..361e3c7
--- /dev/null
+++ b/unittest_stack.c
@@ -0,0 +1,197 @@
+
+#include <stdio.h>
+#include <stdlib.h>
+#include "stack.h"
+#include "unity.h"
+
+
+void test_createMatrixFailsOnZeroDimensions(void)
+{
+    Matrix matrixToTest1 = createMatrix(0, 1);
+    Matrix matrixToTest2 = createMatrix(1, 0);
+    TEST_ASSERT_NULL(matrixToTest1.buffer);
+    TEST_ASSERT_EQUAL_UINT32(0, matrixToTest1.rows);
+    TEST_ASSERT_EQUAL_UINT32(0, matrixToTest1.cols);
+    TEST_ASSERT_NULL(matrixToTest2.buffer);
+    TEST_ASSERT_EQUAL_UINT32(0, matrixToTest2.rows);
+    TEST_ASSERT_EQUAL_UINT32(0, matrixToTest2.cols);
+}
+
+void test_createMatrixReturnsCorrectMatrixDimensions(void)
+{
+    const unsigned int expectedRows = 15;
+    const unsigned int expectedCols = 10;
+    
+    Matrix matrixToTest = createMatrix(expectedRows, expectedCols);
+    TEST_ASSERT_EQUAL_UINT32(expectedRows, matrixToTest.rows);
+    TEST_ASSERT_EQUAL_UINT32(expectedCols, matrixToTest.cols);
+    free(matrixToTest.buffer);
+}
+
+void test_clearMatrixSetsMembersToNull(void)
+{
+    Matrix matrixToTest = createMatrix(10, 10);
+    clearMatrix(&matrixToTest);
+    TEST_ASSERT_NULL(matrixToTest.buffer);
+    TEST_ASSERT_EQUAL_UINT32(0, matrixToTest.rows);
+    TEST_ASSERT_EQUAL_UINT32(0, matrixToTest.cols);
+}
+
+void test_addReturnsCorrectResult(void)
+{
+    MatrixType buffer1[] = {1, 2, 3, 4, 5, 6};
+    MatrixType buffer2[] = {7, 8, 9, 10, 11, 12};
+    Matrix matrix1 = {.rows=2, .cols=3, .buffer=buffer1};
+    Matrix matrix2 = {.rows=2, .cols=3, .buffer=buffer2};
+
+    Matrix result = add(matrix1, matrix2);
+
+    float expectedResults[] = {8, 10, 12, 14, 16, 18};
+
+    TEST_ASSERT_EQUAL_UINT32(matrix1.rows, result.rows);
+    TEST_ASSERT_EQUAL_UINT32(matrix2.rows, result.rows);
+    TEST_ASSERT_EQUAL_UINT32(matrix1.cols, result.cols);
+    TEST_ASSERT_EQUAL_UINT32(matrix2.cols, result.cols);
+    TEST_ASSERT_EQUAL_INT(sizeof(expectedResults)/sizeof(expectedResults[0]), result.rows * result.cols);
+    TEST_ASSERT_EQUAL_FLOAT_ARRAY(expectedResults, result.buffer, result.cols * result.rows);
+    free(result.buffer);
+}
+
+void test_addFailsOnDifferentInputDimensions(void)
+{
+    MatrixType buffer1[] = {1, 2, 3, 4, 5, 6};
+    MatrixType buffer2[] = {7, 8, 9, 10, 11, 12};
+    Matrix matrix1 = {.rows=2, .cols=3, .buffer=buffer1};
+    Matrix matrix2 = {.rows=3, .cols=2, .buffer=buffer2};
+    
+    Matrix result = add(matrix1, matrix2);
+
+    TEST_ASSERT_NULL(result.buffer);
+    TEST_ASSERT_EQUAL_UINT32(0, result.rows);
+    TEST_ASSERT_EQUAL_UINT32(0, result.cols);
+}
+
+void test_addSupportsBroadcasting(void)
+{
+    MatrixType buffer1[] = {1, 2, 3, 4, 5, 6};
+    MatrixType buffer2[] = {7, 8};
+    Matrix matrix1 = {.rows=2, .cols=3, .buffer=buffer1};
+    Matrix matrix2 = {.rows=2, .cols=1, .buffer=buffer2};
+
+    Matrix result1 = add(matrix1, matrix2);
+    Matrix result2 = add(matrix2, matrix1);
+
+    float expectedResults[] = {8, 9, 10, 12, 13, 14};
+
+    TEST_ASSERT_EQUAL_UINT32(matrix1.rows, result1.rows);
+    TEST_ASSERT_EQUAL_UINT32(matrix1.cols, result1.cols);
+    TEST_ASSERT_EQUAL_UINT32(matrix1.rows, result2.rows);
+    TEST_ASSERT_EQUAL_UINT32(matrix1.cols, result2.cols);
+
+    TEST_ASSERT_EQUAL_INT(sizeof(expectedResults)/sizeof(expectedResults[0]), result1.rows * result1.cols);
+    TEST_ASSERT_EQUAL_FLOAT_ARRAY(expectedResults, result1.buffer, result1.cols * result1.rows);
+    TEST_ASSERT_EQUAL_INT(sizeof(expectedResults)/sizeof(expectedResults[0]), result2.rows * result2.cols);
+    TEST_ASSERT_EQUAL_FLOAT_ARRAY(expectedResults, result2.buffer, result2.cols * result2.rows);
+
+    free(result1.buffer);
+    free(result2.buffer);
+}
+
+void test_multiplyReturnsCorrectResults(void)
+{
+    MatrixType buffer1[] = {1, 2, 3, 4, 5, 6};
+    MatrixType buffer2[] = {7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18};
+    Matrix matrix1 = {.rows=2, .cols=3, .buffer=buffer1};
+    Matrix matrix2 = {.rows=3, .cols=4, .buffer=buffer2};
+    
+    Matrix result = multiply(matrix1, matrix2);
+
+    float expectedResults[] = {74, 80, 86, 92, 173, 188, 203, 218};
+
+    TEST_ASSERT_EQUAL_UINT32(matrix1.rows, result.rows);
+    TEST_ASSERT_EQUAL_UINT32(matrix2.cols, result.cols);
+    TEST_ASSERT_EQUAL_INT(sizeof(expectedResults)/sizeof(expectedResults[0]), result.rows * result.cols);
+    TEST_ASSERT_EQUAL_FLOAT_ARRAY(expectedResults, result.buffer, result.cols * result.rows);
+
+    free(result.buffer);
+}
+
+void test_multiplyFailsOnWrongInputDimensions(void)
+{
+    MatrixType buffer1[] = {1, 2, 3, 4, 5, 6};
+    MatrixType buffer2[] = {7, 8, 9, 10, 11, 12};
+    Matrix matrix1 = {.rows=2, .cols=3, .buffer=buffer1};
+    Matrix matrix2 = {.rows=2, .cols=3, .buffer=buffer2};
+
+    Matrix result = multiply(matrix1, matrix2);
+
+    TEST_ASSERT_NULL(result.buffer);
+    TEST_ASSERT_EQUAL_UINT32(0, result.rows);
+    TEST_ASSERT_EQUAL_UINT32(0, result.cols);
+}
+
+void test_getMatrixAtReturnsCorrectResult(void)
+{
+    MatrixType buffer[] = {1, 2, 3, 4, 5, 6};
+    Matrix matrixToTest = {.rows=2, .cols=3, .buffer=buffer};
+    int expectedResult = buffer[4];
+
+    TEST_ASSERT_EQUAL_INT(expectedResult, getMatrixAt(matrixToTest, 1, 1));
+}
+
+void test_getMatrixAtFailsOnIndicesOutOfRange(void)
+{
+    MatrixType buffer[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
+    Matrix matrixToTest = {.rows=2, .cols=3, .buffer=buffer};
+
+    TEST_ASSERT_EQUAL_INT(UNDEFINED_MATRIX_VALUE, getMatrixAt(matrixToTest, 2, 3));
+}
+
+void test_setMatrixAtSetsCorrectValue(void)
+{
+    const int expectedResult = -1;
+    MatrixType buffer[] = {1, 2, 3, 4, 5, 6};
+    Matrix matrixUnderTest = {.rows=2, .cols=3, .buffer=buffer};
+
+    setMatrixAt(expectedResult, matrixUnderTest, 1, 2);
+    TEST_ASSERT_EQUAL_INT(expectedResult, buffer[5]);
+}
+
+void test_setMatrixAtFailsOnIndicesOutOfRange(void)
+{
+    const float expectedResults[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
+    MatrixType buffer[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
+    Matrix matrixToTest = {.rows=2, .cols=3, .buffer=buffer};
+
+    setMatrixAt(-1, matrixToTest, 2, 3);
+    TEST_ASSERT_EQUAL_FLOAT_ARRAY(expectedResults, matrixToTest.buffer, sizeof(buffer)/sizeof(MatrixType));
+}
+
+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("============================\nMatrix tests\n============================\n");
+    RUN_TEST(test_createMatrixReturnsCorrectMatrixDimensions);
+    RUN_TEST(test_createMatrixFailsOnZeroDimensions);
+    RUN_TEST(test_clearMatrixSetsMembersToNull);
+    RUN_TEST(test_addReturnsCorrectResult);
+    RUN_TEST(test_addFailsOnDifferentInputDimensions);
+    RUN_TEST(test_addSupportsBroadcasting);
+    RUN_TEST(test_multiplyReturnsCorrectResults);
+    RUN_TEST(test_multiplyFailsOnWrongInputDimensions);
+    RUN_TEST(test_getMatrixAtReturnsCorrectResult);
+    RUN_TEST(test_getMatrixAtFailsOnIndicesOutOfRange);
+    RUN_TEST(test_setMatrixAtSetsCorrectValue);
+    RUN_TEST(test_setMatrixAtFailsOnIndicesOutOfRange);
+
+    return UNITY_END();
+}
\ No newline at end of file