well, nothing works, at least there is something to debug

src/main.c

@@ -1,7 +1,17 @@
+#include "lexer.h"
+#include "parser.h"
 #include <stdlib.h>
 #include <stdio.h>
 
-int main(int argc, char *argv[]) {
-    puts("Hello");
+int main(void) {
+    ASTNodeArray context;
+
+    tokenize("3 + 4 * 5", &context);
+
+    AST tree = parse(&context);
+    print_AST(tree);
+
+    printf("Hola\n");
+
     return EXIT_SUCCESS;
 }

src/parser.c

@@ -107,7 +107,9 @@ void print_AST(AST tree) {
 }
 
 void print_node(ASTNode *node, int depth) {
-    if (!node) return;
+    if (node == NULL) {
+        return;
+    }
 
     if (node->type == NODE_BINARY_OP) {
         print_node(node->data.binary.right, depth + 1);

test/CMakeLists.txt

@@ -2,6 +2,7 @@ find_package(cmocka REQUIRED)
 
 add_executable(test_nodeArray test_ASTNodeArray.c)
 add_executable(test_lexer test_lexer.c)
+add_executable(test_parser test_parser.c)
 
 target_link_libraries(test_nodeArray
     calculator_lib
@@ -13,5 +14,11 @@ target_link_libraries(test_lexer
     cmocka::cmocka
 )
 
+target_link_libraries(test_parser
+    calculator_lib
+    cmocka::cmocka
+)
+
 add_test(NAME nodeArray_tests COMMAND test_nodeArray)
 add_test(NAME lexer_tests COMMAND test_lexer)
+add_test(NAME parser_tests COMMAND test_parser)

test/test_parser.c

@@ -1,5 +1,58 @@
-#include <stdlib.h>
+#include "lexer.h"
+#include "parser.h"
+#include <stdarg.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <setjmp.h>
+#include <cmocka.h>
 
-int main() {
-    return EXIT_SUCCESS;
+static void test_parsing_basic_expression(void **state) {
+    (void) state;
+
+    char expr[256] = "2 + 3 / 66 * 789";
+    ASTNodeArray tokens;
+    ASTNode node;
+    
+    assert_int_equal(tokenize(expr, &tokens), LEXER_OK);
+    assert_int_equal(tokens.len, 7);
+
+    ASTNodeArray_get(&tokens, 0, &node);
+    assert_int_equal(node.type, NODE_INTEGER);
+    assert_int_equal(node.data.integer, 2);
+
+    ASTNodeArray_get(&tokens, 1, &node);
+    assert_int_equal(node.type, NODE_BINARY_OP);
+    assert_int_equal(node.data.binary.op, OP_ADD);
+
+    ASTNodeArray_get(&tokens, 2, &node);
+    assert_int_equal(node.type, NODE_INTEGER);
+    assert_int_equal(node.data.integer, 3);
+
+    ASTNodeArray_get(&tokens, 3, &node);
+    assert_int_equal(node.type, NODE_BINARY_OP);
+    assert_int_equal(node.data.binary.op, OP_DIV);
+
+    ASTNodeArray_get(&tokens, 4, &node);
+    assert_int_equal(node.type, NODE_INTEGER);
+    assert_int_equal(node.data.integer, 66);
+
+    ASTNodeArray_get(&tokens, 5, &node);
+    assert_int_equal(node.type, NODE_BINARY_OP);
+    assert_int_equal(node.data.binary.op, OP_MUL);
+
+    ASTNodeArray_get(&tokens, 6, &node);
+    assert_int_equal(node.type, NODE_INTEGER);
+    assert_int_equal(node.data.integer, 789);
+
+    AST tree = parse(&tokens);
+    assert_int_equal(tree.head->type, NODE_BINARY_OP);
+}
+
+int main(void) {
+    const struct CMUnitTest tests [] = {
+        cmocka_unit_test(test_parsing_basic_expression),
+    };
+
+    return cmocka_run_group_tests(tests, NULL, NULL);
 }