test: add additional tests around swapping and iterators

test/iterator-ops.cpp

@@ -0,0 +1,24 @@
+#include <vector>
+#include <cassert>
+#include <ring-buffer.h>
+
+int main() {
+    ring_buffer<int, 4> buf;
+
+    buf.push_back(1);
+    buf.push_back(2);
+    buf.push_back(3);
+    buf.push_back(4);
+    buf.push_back(5);
+    buf.push_back(6);
+
+    {
+        auto it = buf.begin();
+        ++it;
+        it++;
+        assert(*it == 5);
+        --it;
+        it--;
+        assert(*it == 3);
+    }
+}