add more tests

test/push-iterate-const.cpp

@@ -0,0 +1,35 @@
+#include <vector>
+#include <cassert>
+#include <ring-buffer.h>
+
+int main() {
+    ring_buffer<int, 4> buf;
+    const ring_buffer<int, 4>& const_buf = 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);
+
+    {
+        std::vector<int> expected{3, 4, 5, 6};
+        std::vector<int> actual;
+        for (const int& i : const_buf) {
+            actual.push_back(i);
+        }
+        assert(actual == expected);
+    }
+
+    buf.push_back(7);
+
+    {
+        std::vector<int> expected{4, 5, 6, 7};
+        std::vector<int> actual;
+        for (const int& i : const_buf) {
+            actual.push_back(i);
+        }
+        assert(actual == expected);
+    }
+}