pub struct Foo {
    a: u64,
    b: i8,
}

impl Foo {
    pub fn new() -> Foo {
        Foo { a: 42, b: 41 }
    }

    pub fn add(&mut self) {
        self.b += 1;
    }

    pub fn dec(&mut self) {
        self.b -= 1;
    }

    pub fn get(&self) -> u64 {
        self.a
    }
}

#[cfg(test)]
mod test {
    use super::*;

    #[test]
    fn add() {
        let mut f = Foo::new();
        f.add();
        assert_eq!(f.b, 42);
    }
}

#[test]
fn it_works() {
}

--- 
+++ 
@@ -1,34 +1,3 @@
-pub struct Foo {
-    a: u64,
-    b: i8,
+#[test]
+fn it_works() {
 }
-
-impl Foo {
-    pub fn new() -> Foo {
-        Foo { a: 42, b: 41 }
-    }
-
-    pub fn add(&mut self) {
-        self.b += 1;
-    }
-
-    pub fn dec(&mut self) {
-        self.b -= 1;
-    }
-
-    pub fn get(&self) -> u64 {
-        self.a
-    }
-}
-
-#[cfg(test)]
-mod test {
-    use super::*;
-
-    #[test]
-    fn add() {
-        let mut f = Foo::new();
-        f.add();
-        assert_eq!(f.b, 42);
-    }
-}
Add some code for coverage testing
