Christian colleges often do not require that students share the same faith as the college itself. They may encourage core Christian beliefs and practices, and the spiritual growth of students will always be a goal at a Christian college, but they cannot force or police students into "being Christian."
Anyone is free to apply to any school they like, including Christian colleges. Some Christian colleges may ask, as part of the application process, what denomination/religious affiliation prospective students fall under. Additionally, they may require a testimony as part of the application, but that doesn't mean that the testimony must end with students being Christian.
As with every college, the students who ultimately attend the school are decided by the Christian college, so the students that are selected are deemed the best fit for the schools based on a variety of reasons.
However, even if a student is not a Christian, they will be held to the same code of conduct as all the other students. Non-Christian students attending a Christian school will be expected to abide by all the rules, curfews, and behavioral expectations that align with the values that the school promotes, even if the students do not agree with those values.
Additionally, if a Christian school requires chapels and theology classes for each student, students that are not Christian are not given exceptions. They will be required to attend the same number of chapels and take the same amount of Theology classes as all other students, regardless of objections to the faith.
Ultimately, most Christian colleges will not turn away a student just because they do not share the Christian faith. However, the expectations and requirements for Spiritual activities will be the same for that student as for every other student. The degree to which activities and classes are required depends on which colleges specifically. To find out what sort of expectations are in place for students, check the website or with the admissions department of the school(s) you are interested in.