test: add additional tests around swapping and iterators

test/swap-ring-buffer-iterator.cpp

@@ -0,0 +1,33 @@
+#include <vector>
+#include <cassert>
+#include <ring-buffer.h>
+#include <utility>
+
+int main() {
+    ring_buffer<int, 4> buf1;
+
+    buf1.push_back(1);
+    buf1.push_back(2);
+    buf1.push_back(3);
+    buf1.push_back(4);
+    buf1.push_back(5);
+    buf1.push_back(6);
+
+    ring_buffer<int, 4> buf2;
+
+    buf2.push_back(10);
+    buf2.push_back(20);
+    buf2.push_back(30);
+    buf2.push_back(40);
+    buf2.push_back(50);
+    buf2.push_back(60);
+
+    auto it1 = buf1.begin();
+    auto it2 = buf2.begin();
+    std::swap(it1, it2);
+
+    {
+        assert(*it1 == 30);
+        assert(*it2 == 3);
+    }
+}