如何在PHPUnit中验证此函数是否为字符串？

Here's the code for my original PHP code:

public function outputText() {   
    $i = 1;   
    foreach($this->sorted_data as $this->data) {   
        echo "$i. ".$this->data[0]."<br/>";   
        $i++;  
    }  
}

And here's the code for the PHPUnit:

public function testVerify() {
    $yn = new SortThisData();
    $yn->readFile("input.txt");
    $output = $yn->outputText();
    $this->assertTrue(is_string($output));

    //if(!is_string($yn->get()))
    //    return false;
    //$this->assertNotEmpty($yn->get());
    }

The class is called SortThisData in the original PHP file. When I used gettype(), it said it was null. I'm trying to verify that it is a string so it can pass in PHPUnit. Is there a way I can do this?

You're looking for assertInternalType().

Update: I didn't realize you were echoing the output. You will probably need to use output buffering to capture the text.

public function testVerify() {
    $yn = new SortThisData();
    $yn->readFile("input.txt");

    // start output buffering and capture the output
    ob_start();
    $yn->outputText();
    $output = ob_get_clean();

    $this->assertInternalType('string', $output);
}

No disagreement with Baylor's answer. To answer the question, as asked, what you had was also good enough:

$this->assertTrue(is_string($output));

Or you could have done:

$this->assertEquals('string',gettype($output));

(The advantage of the latter is, when it fails, it will also tell you the type of $output; assertTrue will only tell you that something failed.)

assertInternalType() does exactly that, but was only introduced in PHPUnit 3.5, and you will still find PHPUnit 3.4 in use on some machines.