Muslims believe that the shahadah is without value unless it is earnest.
From the en.wikipedia.org
The entire song is nothing but repetition of God's names and the shahadah, or testimony of faith.
From the blog.beliefnet.com
It is the shahadah that welcomes Muslim newborns into this world, and it is the same shahadah that marks their transition to the life beyond.
From the newsobserver.com
Islamic scholars have therefore developed, based on the data of the Quran and hadith, essential criteria for an expression of the shahadah to be earnest.
From the en.wikipedia.org
A person is considered to have converted to Islam from the moment he or she sincerely makes this declaration of faith, called the shahadah.
From the en.wikipedia.org
Islamic sites fulfill a number of distinct roles, such as providing advice concerning religious doctrine, download daily prayers and for taking the shahadah over the Internet.
From the en.wikipedia.org
More examples
The first pillar of Islam is an affirmation of faith
Sunni theological traditions
Declaration of faith. A person must recite the shahadah to convert to Islam. The shahadah in Islam is:: "I testify that there is no god but Allah and I testify that Muhammad is the Messenger of Allah."
The Testimony that there is none worthy of worship except God and that Muhammad is His messenger.
The testimony of faith: La ilaha illa Allah. Muhammadun rasulullah. ("There is no God but God. Muhammad is the messenger of God."). The first Pillar of Islam
The testimony of faith "Laa ilaha ill'Allah. Muhammadan rasul Allah" that makes a person a Muslim under the law