diff --git a/cmd/benchcmp/benchcmp_test.go b/cmd/benchcmp/benchcmp_test.go
index 2226079..b79bfaa 100644
--- a/cmd/benchcmp/benchcmp_test.go
+++ b/cmd/benchcmp/benchcmp_test.go
@@ -57,3 +57,27 @@
 		t.Errorf("filtered bench set incorrectly, want %v have %v", want, have)
 	}
 }
+
+func TestFormatNs(t *testing.T) {
+	tests := []struct {
+		input    float64
+		expected string
+	}{
+		{input: 0, expected: "0.00"},
+		{input: 0.2, expected: "0.20"},
+		{input: 2, expected: "2.00"},
+		{input: 2.2, expected: "2.20"},
+		{input: 4, expected: "4.00"},
+		{input: 16, expected: "16.0"},
+		{input: 16.08, expected: "16.1"},
+		{input: 128, expected: "128"},
+		{input: 256.2, expected: "256"},
+	}
+
+	for _, tt := range tests {
+		actual := formatNs(tt.input)
+		if actual != tt.expected {
+			t.Fatalf("%f. got %q, want %q", tt.input, actual, tt.expected)
+		}
+	}
+}