diff --git a/src/instruments/instrument.rs b/src/instruments/instrument.rs
new file mode 100644
index 0000000..09d64b2
--- /dev/null
+++ b/src/instruments/instrument.rs
@@ -0,0 +1,10 @@
+use crate::money::{Currency, Money};
+
+pub trait Instrument<C>
+where
+    C: Currency,
+{
+    fn npv(&self) -> Money<C>;
+
+    // TODO:set_pricing_engine(Rc<PricingEngine>)
+}
diff --git a/src/instruments/mod.rs b/src/instruments/mod.rs
index 4835d72..a0c6540 100644
--- a/src/instruments/mod.rs
+++ b/src/instruments/mod.rs
@@ -1,3 +1,6 @@
+pub mod instrument;
+pub use instrument::Instrument;
+
 pub mod options;
 
 pub mod exercises;
diff --git a/src/instruments/options/european_option.rs b/src/instruments/options/european_option.rs
index 95ad365..9dafc20 100644
--- a/src/instruments/options/european_option.rs
+++ b/src/instruments/options/european_option.rs
@@ -86,6 +86,7 @@ mod tests {
 
         assert_eq!(call.to_string(), "2024/07/27 $ 30.00 C (E)");
         assert_eq!(put.to_string(), "2024/07/27 $ 30.00 P (E)");
+        assert_eq!(call.get_strike(), strike_price);
         assert_eq!(call.get_payoff().to_string(), "$ 30.00 CALL");
         assert_eq!(
             call.get_exercise().get_dates(),
diff --git a/src/lib.rs b/src/lib.rs
index 7468297..673d329 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,18 +1,25 @@
 #![warn(clippy::all)]
 
 pub mod instruments;
+
 pub mod money;
+// pub use money::{currency, Currency, ExchangeRate, Money};
 
 #[macro_use]
 pub(crate) mod macros;
 
 pub mod interest_rate;
+pub use interest_rate::{implied_rate_from_compound_factor, InterestRate};
+
 pub mod term_structures;
 
 pub mod compounding;
+pub use compounding::Compounding;
+
 pub mod time;
 
 pub mod types;
+pub use types::{CompoundFactor, DiscountFactor, MonetaryNumber, Percentage, Strike, Volatility};
 
 pub mod math;
 
diff --git a/src/math/interpolation/linear_interpolator.rs b/src/math/interpolation/linear_interpolator.rs
index 63d6c70..d2ec831 100644
--- a/src/math/interpolation/linear_interpolator.rs
+++ b/src/math/interpolation/linear_interpolator.rs
@@ -159,6 +159,17 @@ mod tests {
 
     #[test]
     fn test_linear_interpolator() {
+        let interpolator: LinearInterpolator<OrderedFloat<f64>, OrderedFloat<f64>> =
+            LinearInterpolator::new();
+        assert_eq!(
+            interpolator.interpolate(OrderedFloat(1.0)),
+            InterpolationResult::NoPoints
+        );
+
+        let interpolator: LinearInterpolator<OrderedFloat<f64>, OrderedFloat<f64>> =
+            LinearInterpolator::default();
+        assert_eq!(interpolator.range(), None);
+
         let data: Vec<(OrderedFloat<f64>, OrderedFloat<f64>)> = vec![
             (OrderedFloat(1.0), OrderedFloat(10.0)),
             (OrderedFloat(2.0), OrderedFloat(20.0)),