Second test, just pop, almost identical to first put important for asserting pop works because it is very needed

include/lexer.h

@@ -7,7 +7,7 @@
 // For identifing
 typedef enum {
     NODE_NUMBER,
-    NODE_OPERATOR,
+    NODE_BINARY_OP,
 } ASTNodeType;
 
 // For classify operators
@@ -41,10 +41,12 @@ typedef struct ASTNode {
     ASTNodeType type;
     union {
         double number;
-        struct ASTNode *left;
-        struct ASTNode *right;
-        Operator op;
-    } operator;
+        struct {
+            struct ASTNode *left;
+            struct ASTNode *right;
+            Operator op;
+        } binary;
+    } data;
 } ASTNode;
 
 // I prefer ot have a dynamic array for storing the "tokens"

test/test_ASTNodeArray.c

@@ -9,20 +9,21 @@
 static void test_array_push(void **state) {
     (void) state;
 
+    // We use 2 to force resize and checking anything wrong with malloc
     ASTNodeArray arr = ASTNodeArray_init(2);
     ASTNode node1 = {
         .type = NODE_NUMBER,
-        .operator = { .number = 90 }
+        .data = { .number = 90 }
     };
 
     ASTNode node2 = {
         .type = NODE_NUMBER,
-        .operator = { .number = 80 }
+        .data = { .number = 80 }
     };
 
     ASTNode node3 = {
         .type = NODE_NUMBER,
-        .operator = { .number = 70 }
+        .data = { .number = 70 }
     };
 
     assert_int_equal(ASTNodeArray_push(&arr, node1), ARRAY_OK);
@@ -35,11 +36,44 @@ static void test_array_push(void **state) {
     assert_int_equal(ASTNodeArray_len(&arr), 3);
 }
 
+static void test_array_pop(void **state) {
+    (void) state;
 
+    ASTNodeArray arr = ASTNodeArray_init(2);
+    ASTNode node1 = {
+        .type = NODE_NUMBER,
+        .data = { .number = 90 }
+    };
+
+    ASTNode node2 = {
+        .type = NODE_NUMBER,
+        .data = { .number = 80 }
+    };
+
+    ASTNode node3 = {
+        .type = NODE_NUMBER,
+        .data = { .number = 70 }
+    };
+
+    assert_int_equal(ASTNodeArray_push(&arr, node1), ARRAY_OK);
+    assert_int_equal(ASTNodeArray_len(&arr), 1);
+
+    assert_int_equal(ASTNodeArray_push(&arr, node2), ARRAY_OK);
+    assert_int_equal(ASTNodeArray_len(&arr), 2);
+
+    assert_int_equal(ASTNodeArray_push(&arr, node3), ARRAY_OK);
+    assert_int_equal(ASTNodeArray_len(&arr), 3);
+
+    ASTNode node4;
+    assert_int_equal(ASTNodeArray_pop(&arr, 1, &node4), ARRAY_OK);
+    assert_int_equal(node4.type, NODE_NUMBER);
+    assert_int_equal(node4.data.number, 80);
+}
 
 int main(void) {
     const struct CMUnitTest tests[] = {
         cmocka_unit_test(test_array_push),
+        cmocka_unit_test(test_array_pop),
     };
 
     return cmocka_run_group_tests(tests, NULL, NULL);