test: improve NAF decomposition test coverage

[DeVikingMark]

Description:

Enhance TestNafDecomposition with comprehensive test cases:

• Add test table with various input numbers
• Add boundary cases (0, 1)
• Add interesting cases requiring NAF conversion
• Add property checks for NAF representation
• Add reconstruction validation
• Improve error messages with detailed information

This commit removes the TODO comment and provides proper test coverage for the NafDecomposition function, ensuring correct NAF properties and accurate number reconstruction.

[yelhousni]

Thanks @DeVikingMark for the test!
There are though two sign errors in 15 and 31 and endianness error in 7. You should also run go fmt utils_test.go to pass CI.

[yelhousni]

it should be {"7", []int8{-1, 0, 0, 1}}

[yelhousni]

it should be {"15", []int8{-1, 0, 0, 0, 1}}

[yelhousni]

it should be {"31", []int8{-1, 0, 0, 0, 0, 1}}

[yelhousni]

Thanks for the test! There are though two sign errors in 15 and 31 and endianness error in 7. You should also run go fmt utils_test.go to pass CI.

Here is the suggested diff:

diff --git a/ecc/utils_test.go b/ecc/utils_test.go
index fed45efe5..187d760df 100644
--- a/ecc/utils_test.go
+++ b/ecc/utils_test.go
@@ -12,12 +12,12 @@ func TestNafDecomposition(t *testing.T) {
 		input    string // large number in decimal form
 		expected []int8 // expected NAF representation
 	}{
-		{"13", []int8{1, 0, -1, 0, 1}},          // existing test case
-		{"0", []int8{}},                          // edge case - zero
-		{"1", []int8{1}},                         // edge case - one
-		{"7", []int8{1, 0, 0, -1}},              // 7 = 2³ - 2⁰ (8 - 1)
-		{"15", []int8{1, 0, 0, 0, 1}},           // 15 = 2⁴ - 2⁰
-		{"31", []int8{1, 0, 0, 0, 0, 1}},        // 31 = 2⁵ - 2⁰
+		{"13", []int8{1, 0, -1, 0, 1}},    // existing test case
+		{"0", []int8{}},                   // edge case - zero
+		{"1", []int8{1}},                  // edge case - one
+		{"7", []int8{-1, 0, 0, 1}},        // 7 = 2³ - 2⁰ (8 - 1)
+		{"15", []int8{-1, 0, 0, 0, 1}},    // 15 = 2⁴ - 2⁰
+		{"31", []int8{-1, 0, 0, 0, 0, 1}}, // 31 = 2⁵ - 2⁰
 	}
 
 	for i, test := range tests {
@@ -33,7 +33,7 @@ func TestNafDecomposition(t *testing.T) {
 
 		// Length check
 		if len(naf) != len(test.expected) {
-			t.Errorf("Test %d: Incorrect length for input %s. Got %d, want %d", 
+			t.Errorf("Test %d: Incorrect length for input %s. Got %d, want %d",
 				i, test.input, len(naf), len(test.expected))
 			continue
 		}
@@ -69,7 +69,7 @@ func TestNafDecomposition(t *testing.T) {
 			power.Mul(power, big.NewInt(2))
 		}
 		if reconstructed.Cmp(input) != 0 {
-			t.Errorf("Test %d: NAF reconstruction failed for input %s. Got %s", 
+			t.Errorf("Test %d: NAF reconstruction failed for input %s. Got %s",
 				i, test.input, reconstructed.String())
 		}
 	}

and a python code to cross check values:

def NAF(x):
	if x == 0:
		return []
	z = 0 if x % 2 == 0 else 2 - (x % 4)
	return NAF( (x-z) // 2 ) + [z]

[DeVikingMark]

@yelhousni fixed, is it fine?