diff --git a/tests/merge_join.rs b/tests/merge_join.rs
new file mode 100644
index 0000000..3280b7d
--- /dev/null
+++ b/tests/merge_join.rs
@@ -0,0 +1,108 @@
+use itertools::EitherOrBoth;
+use itertools::free::merge_join_by;
+
+#[test]
+fn empty() {
+    let left: Vec<u32> = vec![];
+    let right: Vec<u32> = vec![];
+    let expected_result: Vec<EitherOrBoth<u32, u32>> = vec![];
+    let actual_result = merge_join_by(left, right, |l, r| l.cmp(r))
+        .collect::<Vec<_>>();
+    assert_eq!(expected_result, actual_result);
+}
+
+#[test]
+fn left_only() {
+    let left: Vec<u32> = vec![1,2,3];
+    let right: Vec<u32> = vec![];
+    let expected_result: Vec<EitherOrBoth<u32, u32>> = vec![
+        EitherOrBoth::Left(1),
+        EitherOrBoth::Left(2),
+        EitherOrBoth::Left(3)
+    ];
+    let actual_result = merge_join_by(left, right, |l, r| l.cmp(r))
+        .collect::<Vec<_>>();
+    assert_eq!(expected_result, actual_result);
+}
+
+#[test]
+fn right_only() {
+    let left: Vec<u32> = vec![];
+    let right: Vec<u32> = vec![1,2,3];
+    let expected_result: Vec<EitherOrBoth<u32, u32>> = vec![
+        EitherOrBoth::Right(1),
+        EitherOrBoth::Right(2),
+        EitherOrBoth::Right(3)
+    ];
+    let actual_result = merge_join_by(left, right, |l, r| l.cmp(r))
+        .collect::<Vec<_>>();
+    assert_eq!(expected_result, actual_result);
+}
+
+#[test]
+fn first_left_then_right() {
+    let left: Vec<u32> = vec![1,2,3];
+    let right: Vec<u32> = vec![4,5,6];
+    let expected_result: Vec<EitherOrBoth<u32, u32>> = vec![
+        EitherOrBoth::Left(1),
+        EitherOrBoth::Left(2),
+        EitherOrBoth::Left(3),
+        EitherOrBoth::Right(4),
+        EitherOrBoth::Right(5),
+        EitherOrBoth::Right(6)
+    ];
+    let actual_result = merge_join_by(left, right, |l, r| l.cmp(r))
+        .collect::<Vec<_>>();
+    assert_eq!(expected_result, actual_result);
+}
+
+#[test]
+fn first_right_then_left() {
+    let left: Vec<u32> = vec![4,5,6];
+    let right: Vec<u32> = vec![1,2,3];
+    let expected_result: Vec<EitherOrBoth<u32, u32>> = vec![
+        EitherOrBoth::Right(1),
+        EitherOrBoth::Right(2),
+        EitherOrBoth::Right(3),
+        EitherOrBoth::Left(4),
+        EitherOrBoth::Left(5),
+        EitherOrBoth::Left(6)
+    ];
+    let actual_result = merge_join_by(left, right, |l, r| l.cmp(r))
+        .collect::<Vec<_>>();
+    assert_eq!(expected_result, actual_result);
+}
+
+#[test]
+fn interspersed_left_and_right() {
+    let left: Vec<u32> = vec![1,3,5];
+    let right: Vec<u32> = vec![2,4,6];
+    let expected_result: Vec<EitherOrBoth<u32, u32>> = vec![
+        EitherOrBoth::Left(1),
+        EitherOrBoth::Right(2),
+        EitherOrBoth::Left(3),
+        EitherOrBoth::Right(4),
+        EitherOrBoth::Left(5),
+        EitherOrBoth::Right(6)
+    ];
+    let actual_result = merge_join_by(left, right, |l, r| l.cmp(r))
+        .collect::<Vec<_>>();
+    assert_eq!(expected_result, actual_result);
+}
+
+#[test]
+fn overlapping_left_and_right() {
+    let left: Vec<u32> = vec![1,3,4,6];
+    let right: Vec<u32> = vec![2,3,4,5];
+    let expected_result: Vec<EitherOrBoth<u32, u32>> = vec![
+        EitherOrBoth::Left(1),
+        EitherOrBoth::Right(2),
+        EitherOrBoth::Both(3, 3),
+        EitherOrBoth::Both(4, 4),
+        EitherOrBoth::Right(5),
+        EitherOrBoth::Left(6)
+    ];
+    let actual_result = merge_join_by(left, right, |l, r| l.cmp(r))
+        .collect::<Vec<_>>();
+    assert_eq!(expected_result, actual_result);
+}