How to test a function which has a setTimeout with jasmine?

The overall approach varies based on your Jasmine version.

Jasmine 1.3

You can use waitsFor:

it( "Disable all submit buttons", function() {
    // Get a button
    var $button = $( '#ai1ec_subscribe_users' );
    // Call the function
    utility_functions.block_all_submit_and_ajax( $button.get(0) );

    // Wait 100ms for all elements to be disabled.
    waitsFor('button to be disabled', function(){
        var found = true;
        // check that all submit are disabled
        $( '#facebook input[type=submit]' ).each( function( i, el ) {
            if (!el.prop('disabled')) found = false;
        });
        return found;
    }, 100);
});

You could also use waits if you know exactly how long it will take:

it( "Disable all submit buttons", function() {
    // Get a button
    var $button = $( '#ai1ec_subscribe_users' );
    // Call the function
    utility_functions.block_all_submit_and_ajax( $button.get(0) );

    // Wait 20ms before running 'runs' section.
    waits(20);

    runs(function(){
        // check that all submit are disabled
        $( '#facebook input[type=submit]' ).each( function( i, el ) {
            expect( el ).toHaveProp( 'disabled', true );
        });
    });
});

There is also a third way of doing this, without the need for waits, waitsFor, and runs.

it( "Disable all submit buttons", function() {
    jasmine.Clock.useMock();

    // Get a button
    var $button = $( '#ai1ec_subscribe_users' );
    // Call the function
    utility_functions.block_all_submit_and_ajax( $button.get(0) );

    jasmine.Clock.tick(10);

    // check that all submit are disabled
    $( '#facebook input[type=submit]' ).each( function( i, el ) {
        expect( el ).toHaveProp( 'disabled', true );
    });
});

Jasmine 2.0

You can use done, the test callback:

it( "Disable all submit buttons", function(done) {
    // Get a button
    var $button = $( '#ai1ec_subscribe_users' );

    utility_functions.block_all_submit_and_ajax( $button.get(0) );

    setTimeout(function(){
        // check that all submit are disabled
        $( '#facebook input[type=submit]' ).each( function( i, el ) {
            expect( el ).toHaveProp( 'disabled', true );
        });

        // Let Jasmine know the test is done.
        done();
    }, 20);
});

you can mock out the timer behavior:

it( "Disable all submit buttons", function() {
    jasmine.clock().install();

    // Get a button
    var $button = $( '#ai1ec_subscribe_users' );
    // Call the function
    utility_functions.block_all_submit_and_ajax( $button.get(0) );

    jasmine.clock().tick(10);

    // check that all submit are disabled
    $( '#facebook input[type=submit]' ).each( function( i, el ) {
        expect( el ).toHaveProp( 'disabled', true );
    });

    jasmine.clock().uninstall()
});