test: add even-function property test for cosh

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---

Author: Payal-Goswami

lib/node_modules/@stdlib/math/base/special/cosh/test/test.js

@@ -44,6 +44,25 @@ tape( 'main export is a function', function test( t ) {
 	t.end();
 });
 
+tape( 'the function is an even function', function test( t ) {
+	var x;
+	var i;
+
+	x = [
+		0.5,
+		1.0,
+		3.5,
+		10.0,
+		50.0,
+		100.0
+	];
+
+	for ( i = 0; i < x.length; i++ ) {
+		t.strictEqual( cosh( x[ i ] ), cosh( -x[ i ] ), 'returns same value for ' + x[ i ] + ' and -' + x[ i ] );
+	}
+	t.end();
+});
+
 tape( 'the function computes the hyperbolic cosine', function test( t ) {
 	var expected;
 	var delta;