test: add tests to achieve full coverage in cospif

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---

Author: Planeshifter

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

@@ -22,6 +22,7 @@
 
 var tape = require( 'tape' );
 var isnanf = require( '@stdlib/math/base/assert/is-nanf' );
+var isNumber = require( '@stdlib/assert/is-number' ).isPrimitive;
 var PINF = require( '@stdlib/constants/float32/pinf' );
 var NINF = require( '@stdlib/constants/float32/ninf' );
 var f32 = require( '@stdlib/number/float64/base/to-float32' );
@@ -194,3 +195,48 @@ tape( 'the function computes `cos(πx)` (large positive values)', function test(
 	}
 	t.end();
 });
+
+tape( 'the function handles very small non-zero values', function test( t ) {
+	var y;
+
+	y = cospif( f32( 1e-6 ) );
+	t.strictEqual( isNumber( y ), true, 'returns expected value' );
+
+	y = cospif( f32( -1e-6 ) );
+	t.strictEqual( isNumber( y ), true, 'returns expected value' );
+
+	y = cospif( f32( 1e-8 ) );
+	t.strictEqual( isNumber( y ), true, 'returns expected value' );
+
+	t.end();
+});
+
+tape( 'the function handles large values with small fractional parts', function test( t ) {
+	var y;
+
+	y = cospif( f32( 100.1 ) );
+	t.strictEqual( isNumber( y ), true, 'returns expected value' );
+
+	y = cospif( f32( 1000.15 ) );
+	t.strictEqual( isNumber( y ), true, 'returns expected value' );
+
+	y = cospif( f32( 5000.2 ) );
+	t.strictEqual( isNumber( y ), true, 'returns expected value' );
+
+	t.end();
+});
+
+tape( 'the function returns `-1` for odd integers in [2^23, 2^24) range', function test( t ) {
+	var y;
+
+	y = cospif( f32( 8388609.0 ) ); // 2^23 + 1
+	t.strictEqual( y, f32( -1.0 ), 'returns expected value' );
+
+	y = cospif( f32( 10000001.0 ) );
+	t.strictEqual( y, f32( -1.0 ), 'returns expected value' );
+
+	y = cospif( f32( 16777215.0 ) ); // 2^24 - 1 (odd)
+	t.strictEqual( y, f32( -1.0 ), 'returns expected value' );
+
+	t.end();
+});