Table cell text going beyond its defined width

I made a table with 4 columns.

Code:

HTML Code:

<table>
<tbody>
<tr>
<td>Testing for long word.Testing for long word.Testing for long word.Testing for long word.Testing for long word.</td>
<td>2</td>
<td>3</td>
<td>4</td>
</tr>
</tbody>
</table>

Css Code:
<s-tyle type="text/css">
table{width:100%;}
td{width:25%;}
</style>

Table looks perfect but when I have a long word with no spaces in the cell, the column goes beyond its 25% that I defined.

Code:

<s-tyle type="text/css">
table{width:100%;table-layout:fixed;border-collapse:collapse}
td{width:25%;overflow:hidden;}
</style>

this works nicely...