nodejs/doc/api/assert.markdown

## Assert

This module is used for writing unit tests for your applications, you can
access it with `require('assert')`.

### assert.fail(actual, expected, message, operator)

Tests if `actual` is equal to `expected` using the operator provided.

### assert.ok(value, [message])

Tests if value is a `true` value, it is equivalent to `assert.equal(true, value, message);`

### assert.equal(actual, expected, [message])

Tests shallow, coercive equality with the equal comparison operator ( `==` ).

### assert.notEqual(actual, expected, [message])

Tests shallow, coercive non-equality with the not equal comparison operator ( `!=` ).

### assert.deepEqual(actual, expected, [message])

Tests for deep equality.

### assert.notDeepEqual(actual, expected, [message])

Tests for any deep inequality.

### assert.strictEqual(actual, expected, [message])

Tests strict equality, as determined by the strict equality operator ( `===` )

### assert.notStrictEqual(actual, expected, [message])

Tests strict non-equality, as determined by the strict not equal operator ( `!==` )

### assert.throws(block, [error], [message])

Expects `block` to throw an error. `error` can be constructor, regexp or 
validation function.

Validate instanceof using constructor:

    assert.throws(
      function() {
        throw new Error("Wrong value");
      },
      Error
    );

Validate error message using RegExp:

    assert.throws(
      function() {
        throw new Error("Wrong value");
      },
      /value/
    );

Custom error validation:

    assert.throws(
      function() {
        throw new Error("Wrong value");
      },
      function(err) {
        if ( (err instanceof Error) && /value/.test(err) ) {
          return true;
        }
      },
      "unexpected error"
    );

### assert.doesNotThrow(block, [error], [message])

Expects `block` not to throw an error, see assert.throws for details.

### assert.ifError(value)

Tests if value is not a false value, throws if it is a true value. Useful when
testing the first argument, `error` in callbacks.