[tree,io] add test for TBasket resize

roottest/root/tree/basket/CMakeLists.txt

@@ -14,5 +14,15 @@ ROOTTEST_ADD_TEST(basket
 # Verify that it does.
 ROOTTEST_ADD_TEST(corrupted_basket
                   COPY_TO_BUILDDIR corrupted.root
-                  COMMAND ${ROOT_root_CMD} -q -l -e "(new TFile(\"corrupted.root\"))->template Get<TTree>(\"tree\")->GetEntry(0)"
+                  COMMAND ${ROOT_root_CMD} -b -q -l -e "(new TFile(\"corrupted.root\"))->template Get<TTree>(\"tree\")->GetEntry(0)"
                   PASSREGEX "Inconsistent length for the entry offset buffer \\(4210752 events for a buffer size of 4\\)")
+
+ROOT_ADD_TEST(test_TBasket_Resize
+   COMMAND ${ROOT_root_CMD} -b -q -l ${CMAKE_CURRENT_SOURCE_DIR}/test_basket_resize.C
+   OUTREF basketresize.ref
+)
+
+ROOT_ADD_TEST(test_TBasket_ReadResetBuffer
+   COMMAND ${ROOT_root_CMD} -b -q -l ${CMAKE_CURRENT_SOURCE_DIR}/test_basket_readreset.C
+   OUTREF basketreadreset.ref
+)

roottest/root/tree/basket/basketreadreset.ref

@@ -0,0 +1,4 @@
+Processing test_basket_readreset.C...
+Initial buffer size: 500000
+Post-reset buffer size is smaller than initial: YES
+Post-reset buffer satisfies safety floor requirement: YES

roottest/root/tree/basket/basketresize.ref

@@ -0,0 +1,2 @@
+Processing test_basket_resize.C...
+Basket buffer size: 100

roottest/root/tree/basket/test_basket_readreset.C

@@ -0,0 +1,61 @@
+#include "TBasket.h"
+#include "TBranch.h"
+#include "TBufferFile.h"
+#include <iostream>
+
+// Subclass to bypass the protected visibility of ReadResetBuffer
+class TestBasket : public TBasket {
+public:
+    TestBasket(TBranch *branch) {
+        fBranch = branch; 
+    }
+
+    void InvokeReadResetBuffer(Int_t basketnumber) {
+        ReadResetBuffer(basketnumber);
+    }
+
+    void SetBufferForTesting(TBuffer *buf) {
+        fBuffer = buf;
+    }
+};
+
+void testTBasketReset() {
+    // Initialize mock environment
+    TBranch dummyBranch;
+    Int_t totalBaskets = 15;
+    dummyBranch.SetBufferEntries(totalBaskets); 
+
+    Int_t currentBasketIdx = 2;
+    Int_t maximumNeededInWindow = 2000; 
+
+    // Setup lookahead window metadata for the next 10 baskets
+    for (int i = 0; i < totalBaskets; ++i) {
+        if (i >= currentBasketIdx && i <= (currentBasketIdx + 10)) {
+            dummyBranch.GetBasketBytes()[i] = maximumNeededInWindow;
+        } else {
+            dummyBranch.GetBasketBytes()[i] = 1000;
+        }
+    }
+
+    TestBasket basket(&dummyBranch);
+
+    // Allocate heavily bloated buffer 
+    Int_t massiveBufferSize = 500000; 
+    TBufferFile* bloatedBuffer = new TBufferFile(TBuffer::kRead, massiveBufferSize);
+    bloatedBuffer->SetBufferOffset(massiveBufferSize);
+    basket.SetBufferForTesting(bloatedBuffer);
+
+    std::cout << "Initial buffer size: " << bloatedBuffer->BufferSize() << std::endl;
+
+    // Trigger the shrinking behavior
+    basket.InvokeReadResetBuffer(currentBasketIdx);
+
+    Int_t postResetSize = bloatedBuffer->BufferSize();
+    std::cout << "Post-reset buffer size is smaller than initial: " 
+              << (postResetSize < massiveBufferSize ? "YES" : "NO") << std::endl;
+
+    std::cout << "Post-reset buffer satisfies safety floor requirement: " 
+              << (postResetSize >= maximumNeededInWindow ? "YES" : "NO") << std::endl;
+
+    delete bloatedBuffer;
+}

roottest/root/tree/basket/test_basket_resize.C

@@ -0,0 +1,25 @@
+#include "TTree.h"
+#include "TMemFile.h"
+#include "TBranch.h"
+#include "TBasket.h"
+#include <iostream>
+
+void test_basket_resize() {
+   TMemFile f("test_resize.root", "RECREATE");
+   TTree tree("T", "Tree for testing basket resizing");
+
+   int value;
+   // Set small initial basket size to force automatic buffer resizing
+   TBranch *branch = tree.Branch("b", &value, "value/I", 64); 
+   for (int i = 0; i < 100; ++i) {
+      value = i;
+      tree.Fill();
+   }
+   tree.Write();
+   TBasket *basket = branch->GetBasket(0);
+   if (basket) {
+      Int_t newSize = basket->GetBufferSize();
+      std::cout << "Basket buffer size: " << newSize << std::endl;
+   }
+   f.Close();
+}