test: add assign tests

---
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    status: passed
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---

Author: headlessNode

lib/node_modules/@stdlib/blas/ext/index-of/lib/assign.js

@@ -131,12 +131,15 @@ function assign( x, searchElement, fromIndex, out, options ) {
 	else if (
 		nargs === 4 &&
 		isndarrayLike( fromIndex ) &&
-		!isndarrayLike( out )
+		!isndarrayLike( out ) &&
+		isObject( out )
 	) {
 		opts = objectAssign( opts, out );
 		out = fromIndex;
 		fromIndex = 0;
-	} else if ( nargs === 5 ) {
+	}
+	// Case: assign( x, searchElement, fromIndex, out, options )
+	else if ( nargs === 5 ) {
 		if ( !isObject( options ) ) {
 			throw new TypeError( format( 'invalid argument. The fifth argument must be an object. Value: `%s`.', options ) );
 		}