Add slicing tests.

src/main.rs

@@ -76,10 +76,16 @@ where
             std::ops::Bound::Unbounded => self.start,
         };
         let new_end = match range.end_bound() {
-            std::ops::Bound::Included(idx) => self.start + idx,
+            std::ops::Bound::Included(idx) => self.start + idx + 1,
-            std::ops::Bound::Excluded(idx) => self.start + idx - 1,
+            std::ops::Bound::Excluded(idx) => self.start + idx,
-            std::ops::Bound::Unbounded => self.start,
+            std::ops::Bound::Unbounded => self.end,
         };
+        if new_start < self.start {
+            panic!("Attempted to extend before the start of the WrappedInput.")
+        }
+        if new_end > self.end {
+            panic!("Attempted to extend past the end of the WrappedInput.")
+        }
 
         // TODO: calculate updated values for WrappedInput
         WrappedInput {
@@ -96,3 +102,60 @@ impl<'s> std::fmt::Display for WrappedInput<'s> {
         Into::<&str>::into(self).fmt(f)
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn range() {
+        let input = WrappedInput::new("foo bar baz");
+        let output = input.slice(4..7);
+        assert_eq!(output.to_string(), "bar");
+    }
+
+    #[test]
+    fn range_to() {
+        let input = WrappedInput::new("foo bar baz");
+        let output = input.slice(..7);
+        assert_eq!(output.to_string(), "foo bar");
+    }
+
+    #[test]
+    fn range_from() {
+        let input = WrappedInput::new("foo bar baz");
+        let output = input.slice(4..);
+        assert_eq!(output.to_string(), "bar baz");
+    }
+
+    #[test]
+    fn full_range() {
+        let input = WrappedInput::new("foo bar baz");
+        let output = input.slice(..);
+        assert_eq!(output.to_string(), "foo bar baz");
+    }
+
+    #[test]
+    fn nested_range() {
+        let input = WrappedInput::new("lorem foo bar baz ipsum");
+        let first_cut = input.slice(6..17);
+        let output = first_cut.slice(4..7);
+        assert_eq!(first_cut.to_string(), "foo bar baz");
+        assert_eq!(output.to_string(), "bar");
+    }
+
+    #[test]
+    #[should_panic]
+    fn out_of_bounds() {
+        let input = WrappedInput::new("lorem foo bar baz ipsum");
+        input.slice(6..30);
+    }
+
+    #[test]
+    #[should_panic]
+    fn out_of_nested_bounds() {
+        let input = WrappedInput::new("lorem foo bar baz ipsum");
+        let first_cut = input.slice(6..17);
+        first_cut.slice(4..14);
+    }
+}