From 32c82f0e675de367903b30b35b82364377614bb4 Mon Sep 17 00:00:00 2001
From: Zsolt Felfoldi <zsfelfoldi@gmail.com>
Date: Tue, 17 Sep 2024 09:56:48 +0200
Subject: [PATCH] core/filtermaps: add filtermaps tests

---
 core/filtermaps/filtermaps_test.go | 112 +++++++++++++++++++++++++++++
 1 file changed, 112 insertions(+)
 create mode 100644 core/filtermaps/filtermaps_test.go

diff --git a/core/filtermaps/filtermaps_test.go b/core/filtermaps/filtermaps_test.go
new file mode 100644
index 000000000000..70a4ce3b14ca
--- /dev/null
+++ b/core/filtermaps/filtermaps_test.go
@@ -0,0 +1,112 @@
+package filtermaps
+
+import (
+	"math/rand"
+	"testing"
+
+	"github.com/ethereum/go-ethereum/common"
+)
+
+func TestSingleMatch(t *testing.T) {
+	for count := 0; count < 100000; count++ {
+		// generate a row with a single random entry
+		mapIndex := rand.Uint32()
+		lvIndex := uint64(mapIndex)<<logValuesPerMap + uint64(rand.Intn(valuesPerMap))
+		var lvHash common.Hash
+		rand.Read(lvHash[:])
+		row := FilterRow{columnIndex(lvIndex, lvHash)}
+		matches := row.potentialMatches(mapIndex, lvHash)
+		// check if it has been reverse transformed correctly
+		if len(matches) != 1 {
+			t.Fatalf("Invalid length of matches (got %d, expected 1)", len(matches))
+		}
+		if matches[0] != lvIndex {
+			if len(matches) != 1 {
+				t.Fatalf("Incorrect match returned (got %d, expected %d)", matches[0], lvIndex)
+			}
+		}
+	}
+}
+
+const (
+	testPmCount = 100
+	testPmLen   = 1000
+)
+
+func TestPotentialMatches(t *testing.T) {
+	var falsePositives int
+	for count := 0; count < testPmCount; count++ {
+		mapIndex := rand.Uint32()
+		lvStart := uint64(mapIndex) << logValuesPerMap
+		var row FilterRow
+		lvIndices := make([]uint64, testPmLen)
+		lvHashes := make([]common.Hash, testPmLen+1)
+		for i := range lvIndices {
+			// add testPmLen single entries with different log value hashes at different indices
+			lvIndices[i] = lvStart + uint64(rand.Intn(valuesPerMap))
+			rand.Read(lvHashes[i][:])
+			row = append(row, columnIndex(lvIndices[i], lvHashes[i]))
+		}
+		// add the same log value hash at the first testPmLen log value indices of the map's range
+		rand.Read(lvHashes[testPmLen][:])
+		for lvIndex := lvStart; lvIndex < lvStart+testPmLen; lvIndex++ {
+			row = append(row, columnIndex(lvIndex, lvHashes[testPmLen]))
+		}
+		// randomly duplicate some entries
+		for i := 0; i < testPmLen; i++ {
+			row = append(row, row[rand.Intn(len(row))])
+		}
+		// randomly mix up order of elements
+		for i := len(row) - 1; i > 0; i-- {
+			j := rand.Intn(i)
+			row[i], row[j] = row[j], row[i]
+		}
+		// check retrieved matches while also counting false positives
+		for i, lvHash := range lvHashes {
+			matches := row.potentialMatches(mapIndex, lvHash)
+			if i < testPmLen {
+				// check single entry match
+				if len(matches) < 1 {
+					t.Fatalf("Invalid length of matches (got %d, expected >=1)", len(matches))
+				}
+				var found bool
+				for _, lvi := range matches {
+					if lvi == lvIndices[i] {
+						found = true
+					} else {
+						falsePositives++
+					}
+				}
+				if !found {
+					t.Fatalf("Expected match not found (got %v, expected %d)", matches, lvIndices[i])
+				}
+			} else {
+				// check "long series" match
+				if len(matches) < testPmLen {
+					t.Fatalf("Invalid length of matches (got %d, expected >=%d)", len(matches), testPmLen)
+				}
+				// since results are ordered, first testPmLen entries should always match exactly
+				for j := 0; j < testPmLen; j++ {
+					if matches[j] != lvStart+uint64(j) {
+						t.Fatalf("Incorrect match at index %d (got %d, expected %d)", j, matches[j], lvStart+uint64(j))
+					}
+				}
+				// the rest are false positives
+				falsePositives += len(matches) - testPmLen
+			}
+		}
+	}
+	// Whenever looking for a certain log value hash, each entry in the row that
+	// was generated by another log value hash (a "foreign entry") has an
+	// 1 / valuesPerMap chance of yielding a false positive.
+	// We have testPmLen unique hash entries and a testPmLen long series of entries
+	// for the same hash. For each of the testPmLen unique hash entries there are
+	// testPmLen*2-1 foreign entries while for the long series there are testPmLen
+	// foreign entries. This means that after performing all these filtering runs,
+	// we have processed 2*testPmLen^2 foreign entries, which given us an estimate
+	// of how many false positives to expect.
+	expFalse := testPmCount * testPmLen * testPmLen * 2 / valuesPerMap
+	if falsePositives < expFalse/2 || falsePositives > expFalse*3/2 {
+		t.Fatalf("False positive rate out of expected range (got %d, expected %d +-50%%)", falsePositives, expFalse)
+	}
+}