test: add tests to achieve full coverage in math/base/special/tanh

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---

Author: Planeshifter

lib/node_modules/@stdlib/math/base/special/tanh/test/test.rational_pq.js

@@ -0,0 +1,70 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2025 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*    http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+'use strict';
+
+// MODULES //
+
+var tape = require( 'tape' );
+var isNumber = require( '@stdlib/assert/is-number' ).isPrimitive;
+var evalrational = require( './../lib/rational_pq.js' );
+
+
+// TESTS //
+
+tape( 'main export is a function', function test( t ) {
+	t.ok( true, __filename );
+	t.strictEqual( typeof evalrational, 'function', 'main export is a function' );
+	t.end();
+});
+
+tape( 'the function evaluates a rational function for x = 0', function test( t ) {
+	var v = evalrational( 0.0 );
+	t.strictEqual( v, -0.3333333333333332, 'returns expected value' );
+	t.end();
+});
+
+tape( 'the function evaluates a rational function for positive values', function test( t ) {
+	var v;
+
+	v = evalrational( 0.5 );
+	t.strictEqual( isNumber( v ), true, 'returns expected value' );
+
+	v = evalrational( 1.0 );
+	t.strictEqual( isNumber( v ), true, 'returns expected value' );
+
+	v = evalrational( 2.0 );
+	t.strictEqual( isNumber( v ), true, 'returns expected value' );
+
+	t.end();
+});
+
+tape( 'the function evaluates a rational function for negative values', function test( t ) {
+	var v;
+
+	v = evalrational( -0.5 );
+	t.strictEqual( isNumber( v ), true, 'returns expected value' );
+
+	v = evalrational( -1.0 );
+	t.strictEqual( isNumber( v ), true, 'returns expected value' );
+
+	v = evalrational( -2.0 );
+	t.strictEqual( isNumber( v ), true, 'returns expected value' );
+
+	t.end();
+});