From 5a42d2af7c799af3db07e80bfbd307d0ea98b8f2 Mon Sep 17 00:00:00 2001
From: x0Lazarus <113273587+x0Lazarus@users.noreply.github.com>
Date: Sat, 26 Sep 2026 01:50:24 -0700
Subject: [PATCH] assert: reject NaN tolerance in InDelta

---
 assert/assertions.go      |  4 ++++
 assert/assertions_test.go | 20 ++++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/assert/assertions.go b/assert/assertions.go
index 166f63726..9358cc1aa 100644
--- a/assert/assertions.go
+++ b/assert/assertions.go
@@ -1456,6 +1456,10 @@ func InDelta(t TestingT, expected, actual interface{}, delta float64, msgAndArgs
 		h.Helper()
 	}
 
+	if math.IsNaN(delta) {
+		return Fail(t, "delta must not be NaN", msgAndArgs...)
+	}
+
 	af, aok := toFloat(expected)
 	bf, bok := toFloat(actual)
 
diff --git a/assert/assertions_test.go b/assert/assertions_test.go
index 11642e096..5708b7c51 100644
--- a/assert/assertions_test.go
+++ b/assert/assertions_test.go
@@ -2339,6 +2339,26 @@ func TestInDelta(t *testing.T) {
 	}
 }
 
+func TestInDeltaNaNDelta(t *testing.T) {
+	t.Parallel()
+
+	for _, tc := range []struct {
+		name             string
+		expected, actual float64
+	}{
+		{"different values", 1, 100},
+		{"equal values", 1, 1},
+		{"NaN values", math.NaN(), math.NaN()},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			mockT := new(mockTestingT)
+			False(t, InDelta(mockT, tc.expected, tc.actual, math.NaN(), "comparison %d", 42))
+			Contains(t, mockT.errorString(), "delta must not be NaN")
+			Contains(t, mockT.errorString(), "comparison 42")
+		})
+	}
+}
+
 func TestInDeltaSlice(t *testing.T) {
 	t.Parallel()