fix: #3512 sign of zero not returning zero in case of a fraction

* sign of zero fraction should return 0/1 instead of 1/1

* moved fraction zero test into correct fraction block

* moved fraction zero test into correct fraction block

Author: kyle-compute

src/function/arithmetic/sign.js

@@ -52,7 +52,7 @@ export const createSign = /* #__PURE__ */ factory(name, dependencies, ({ typed,
     },
 
     Fraction: function (x) {
-      return new Fraction(x.s)
+      return x.n === 0n ? new Fraction(0) : new Fraction(x.s)
     },
 
     // deep map collection, skip zeros since sign(0) = 0

test/unit-tests/function/arithmetic/sign.test.js

@@ -37,6 +37,7 @@ describe('sign', function () {
     assert.strictEqual(math.sign(a).toString(), '1')
     assert.strictEqual(math.sign(fraction(-0.5)).toString(), '-1')
     assert.strictEqual(a.toString(), '0.5')
+    assert.deepStrictEqual(math.sign(math.fraction(0)), math.fraction(0))
   })
 
   it('should calculate the sign of a complex value', function () {