tests: initial internal and integration tests

* src/lib.rs: examples for internel tests
* tests/integration_tests.rs: examples for external callable tests

Signed-off-by: Ralf Zerres <ralf.zerres@networkx.de>

src/lib.rs

@@ -0,0 +1,33 @@
+// This function adds two integers (given as arguments) and returns the sum.
+//
+// # Examples
+//
+// ```
+// assert_eq!(8, advotracker::internal_adder(4, 4));
+// ```
+
+fn internal_adder(a: i32, b: i32) -> i32 {
+    a + b
+}
+
+/// This function adds two to its argument.
+///
+/// # Examples
+///
+/// ```
+/// assert_eq!(4, advotracker::add_two(2));
+/// ```
+
+pub fn add_two(a: i32) -> i32 {
+    internal_adder(a, 2)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn internal_test() {
+        assert_eq!(8, internal_adder(4, 4));
+    }
+}