diff --git a/libqpdf/NNTree.cc b/libqpdf/NNTree.cc
index da97536..0ac4576 100644
--- a/libqpdf/NNTree.cc
+++ b/libqpdf/NNTree.cc
@@ -866,15 +866,14 @@ NNTreeImpl::findInternal(QPDFObjectHandle const& key, bool return_prev_if_not_fo
 }
 
 NNTreeImpl::iterator
-NNTreeImpl::insertFirst(QPDFObjectHandle key, QPDFObjectHandle value)
+NNTreeImpl::insertFirst(QPDFObjectHandle const& key, QPDFObjectHandle const& value)
 {
     auto iter = begin();
     QPDFObjectHandle items;
     if (iter.node.isDictionary()) {
         items = iter.node.getKey(details.itemsKey());
     }
-    if (!(items.isArray())) {
-        QTC::TC("qpdf", "NNTree no valid items node in insertFirst");
+    if (!items.isArray()) {
         error(oh, "unable to find a valid items node");
     }
     items.insertItem(0, key);
@@ -886,30 +885,26 @@ NNTreeImpl::insertFirst(QPDFObjectHandle key, QPDFObjectHandle value)
 }
 
 NNTreeImpl::iterator
-NNTreeImpl::insert(QPDFObjectHandle key, QPDFObjectHandle value)
+NNTreeImpl::insert(QPDFObjectHandle const& key, QPDFObjectHandle const& value)
 {
     auto iter = find(key, true);
     if (!iter.valid()) {
-        QTC::TC("qpdf", "NNTree insert inserts first");
         return insertFirst(key, value);
     } else if (details.compareKeys(key, iter->first) == 0) {
-        QTC::TC("qpdf", "NNTree insert replaces");
         auto items = iter.node.getKey(details.itemsKey());
         items.setArrayItem(iter.item_number + 1, value);
         iter.updateIValue();
     } else {
-        QTC::TC("qpdf", "NNTree insert inserts after");
         iter.insertAfter(key, value);
     }
     return iter;
 }
 
 bool
-NNTreeImpl::remove(QPDFObjectHandle key, QPDFObjectHandle* value)
+NNTreeImpl::remove(QPDFObjectHandle const& key, QPDFObjectHandle* value)
 {
     auto iter = find(key, false);
     if (!iter.valid()) {
-        QTC::TC("qpdf", "NNTree remove not found");
         return false;
     }
     if (value) {
diff --git a/libqpdf/qpdf/NNTree.hh b/libqpdf/qpdf/NNTree.hh
index ed9ac87..c904703 100644
--- a/libqpdf/qpdf/NNTree.hh
+++ b/libqpdf/qpdf/NNTree.hh
@@ -100,9 +100,9 @@ class NNTreeImpl
     iterator end();
     iterator last();
     iterator find(QPDFObjectHandle key, bool return_prev_if_not_found = false);
-    iterator insertFirst(QPDFObjectHandle key, QPDFObjectHandle value);
-    iterator insert(QPDFObjectHandle key, QPDFObjectHandle value);
-    bool remove(QPDFObjectHandle key, QPDFObjectHandle* value = nullptr);
+    iterator insertFirst(QPDFObjectHandle const& key, QPDFObjectHandle const& value);
+    iterator insert(QPDFObjectHandle const& key, QPDFObjectHandle const& value);
+    bool remove(QPDFObjectHandle const& key, QPDFObjectHandle* value = nullptr);
 
     // Change the split threshold for easier testing. There's no real reason to expose this to
     // downstream tree helpers, but it has to be public so we can call it from the test suite.
diff --git a/qpdf/qpdf.testcov b/qpdf/qpdf.testcov
index 0e934f0..f867d13 100644
--- a/qpdf/qpdf.testcov
+++ b/qpdf/qpdf.testcov
@@ -524,11 +524,7 @@ NNTree deepen: loop 0
 NNTree skip invalid kid 0
 NNTree skip item at end of short items 0
 NNTree skip invalid key 0
-NNTree no valid items node in insertFirst 0
 NNTree deepen found empty 0
-NNTree insert inserts first 0
-NNTree insert replaces 0
-NNTree insert inserts after 0
 NNTree unable to determine limits 0
 NNTree warn indirect kid 0
 NNTree fix indirect kid 0
@@ -547,7 +543,6 @@ NNTree node is not a dictionary 0
 NNTree limits didn't change 0
 NNTree increment end() 0
 NNTree insertAfter inserts first 0
-NNTree remove not found 0
 NNTree remove reset limits 0
 NNTree erased last item 0
 NNTree erased non-last item 0