tests: unit: add parsing tests

tests/unit/common.c

@@ -0,0 +1,15 @@
+#include <criterion/redirect.h>
+
+void redirect_streams(void)
+{
+    cr_redirect_stdin();
+    cr_redirect_stdout();
+    cr_redirect_stderr();
+}
+
+void write_to_stdin(const char *input)
+{
+    FILE *f = cr_get_redirected_stdin();
+    fputs(input, f);
+    fclose(f); // Make sure to send EOF when parsing
+}