test: add signed zero tests

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---

Author: kgryte

lib/node_modules/@stdlib/blas/ext/base/gsum/test/test.ndarray.js

@@ -105,6 +105,17 @@ tape( 'the function preserves the sign of zero', function test( t ) {
 	t.end();
 });
 
+tape( 'the function preserves the sign of zero (accessors)', function test( t ) {
+	var x;
+	var v;
+
+	x = [ -0.0, -0.0, -0.0, -0.0, -0.0 ];
+	v = gsum( x.length, toAccessorArray( x ), 1, 0 );
+	t.strictEqual( isNegativeZero( v ), true, 'returns expected value' );
+
+	t.end();
+});
+
 tape( 'if provided an `N` parameter less than or equal to `0`, the function returns `0.0`', function test( t ) {
 	var x;
 	var v;