Use to compare a template with its sandbox. Pass the raw code in nowikis as the first unnamed parameter; the existing template as the second, and the sandbox as the third. The optional named parameter |id= is used as a heading (to describe the test being performed); if |id= is omitted, parameter 1 is used. The optional named parameter |layout= determines whether the live and sandbox outputs are displayed side by side or on top of each other. The default value is vertical (on top of each other). A value of horizontal will produce side by side output.

If the pair of test codes in parameters 2 and 3 both produce the same output, then the test case is displayed in a collapsed table with a green heading. If the test codes produce different output (this includes white space differences), then the test is displayed in an uncollapsed table with a yellow heading.

Note that some more complex templates may cause testcases to be highlighted even when their output is the same. The cause of this is under investigation...

{{testcase
|id=title and url
|layout=vertical
|<nowiki>{{citation|title=Test|url=http://example.org}}</nowiki>
|{{citation        |title=Test|url=http://example.org}}
|{{citation/sandbox|title=Test|url=http://example.org}}
}}

If the sandbox code in parameter 3 gives the same output as the non-sandbox code in parameter 2:

If sandbox gives different output:

title and url
{{citation|title=Test|url=http://example.org}}
Test 
Test  content of the differing output