test: add missing tests

PR-URL: #2701
Ref: 62e247d#commitcomment-144735358
Ref: 62e247d#r144735333
Reviewed-by: Athan Reines <[email protected]>

Author: gunjjoshi

lib/node_modules/@stdlib/math/base/special/powm1/lib/main.js

@@ -121,7 +121,7 @@ function powm1( b, x ) {
 	}
 	result = pow( b, x ) - 1.0;
 	if ( isinfinite( result ) || isnan( result ) ) {
-		return 0.0 / 0.0; // NaN
+		return NaN;
 	}
 	return result;
 }

lib/node_modules/@stdlib/math/base/special/powm1/test/test.js

@@ -141,3 +141,9 @@ tape( 'the function returns `NaN` if provided a `NaN` for the base', function te
 	t.equal( isnan( y ), true, 'returns NaN' );
 	t.end();
 });
+
+tape( 'the function returns `NaN` if provided a `1e308` for the base and `2.0` for the exponent', function test( t ) {
+	var y = powm1( 1e308, 2.0 );
+	t.equal( isnan( y ), true, 'returns expected value' );
+	t.end();
+});

lib/node_modules/@stdlib/math/base/special/powm1/test/test.native.js

@@ -150,3 +150,9 @@ tape( 'the function returns `NaN` if provided a `NaN` for the base', opts, funct
 	t.equal( isnan( y ), true, 'returns expected value' );
 	t.end();
 });
+
+tape( 'the function returns `NaN` if provided a `1e308` for the base and `2.0` for the exponent', opts, function test( t ) {
+	var y = powm1( 1e308, 2.0 );
+	t.equal( isnan( y ), true, 'returns expected value' );
+	t.end();
+});