diff --git a/src/backup.rs b/src/backup.rs
new file mode 100644
index 0000000..b06ecb8
--- /dev/null
+++ b/src/backup.rs
@@ -0,0 +1,46 @@
+use std::io;
+use std::path::Path;
+use walkdir::DirEntry;
+use walkdir::WalkDir;
+use std::fs;
+
+pub struct BackupEngine<'a> {
+    source_path: &'a Path,
+    repository_path: &'a Path,
+}
+
+impl<'a> BackupEngine<'a> {
+    pub fn new(source_path: &'a Path, repository_path: &'a Path) -> Self {
+        BackupEngine {
+            source_path,
+            repository_path,
+        }
+    }
+
+    pub fn backup(&self) -> Result<(), io::Error> {
+        let walker = WalkDir::new(self.source_path);
+        for maybe_entry in walker {
+            let entry = maybe_entry?;
+            if entry.path() != self.source_path {
+                self.process_entry(&entry)?;
+            }
+        }
+        Ok(())
+    }
+
+    pub fn file_version(&self, path: &Path) -> u64 {
+        0
+    }
+
+    fn process_entry(&self, entry: &DirEntry) -> Result<(), io::Error> {
+
+        if entry.file_type().is_dir() {
+            fs::create_dir(self.repository_path.join(entry.file_name()))?;
+        }
+        if entry.file_type().is_file() {
+            fs::copy(entry.path(), self.repository_path.join(entry.file_name()))?;
+        }
+        Ok(())
+    }
+}
+
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..b212788
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,9 @@
+extern crate core;
+#[cfg(test)]
+extern crate dir_diff;
+#[cfg(test)]
+extern crate tempfile;
+extern crate walkdir;
+
+pub mod backup;
+pub mod restore;
diff --git a/src/main.rs b/src/main.rs
index 2254de1..ce1caeb 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,206 +1,3 @@
-extern crate core;
-#[cfg(test)]
-extern crate dir_diff;
-#[cfg(test)]
-extern crate tempfile;
-extern crate walkdir;
-
-use std::fs;
-use std::io;
-use std::path::Path;
-use walkdir::DirEntry;
-use walkdir::WalkDir;
-
-struct BackupEngine<'a> {
-    source_path: &'a Path,
-    repository_path: &'a Path,
-}
-
-impl<'a> BackupEngine<'a> {
-    fn new(source_path: &'a Path, repository_path: &'a Path) -> Self {
-        BackupEngine {
-            source_path,
-            repository_path,
-        }
-    }
-
-    fn backup(&self) -> Result<(), io::Error> {
-        let walker = WalkDir::new(self.source_path);
-        for maybe_entry in walker {
-            let entry = maybe_entry?;
-            if entry.path() != self.source_path {
-                self.process_entry(&entry)?;
-            }
-        }
-        Ok(())
-    }
-
-    fn file_version(&self, path: &Path) -> u64 {
-        0
-    }
-
-    fn process_entry(&self, entry: &DirEntry) -> Result<(), io::Error> {
-
-        if entry.file_type().is_dir() {
-            fs::create_dir(self.repository_path.join(entry.file_name()))?;
-        }
-        if entry.file_type().is_file() {
-            fs::copy(entry.path(), self.repository_path.join(entry.file_name()))?;
-        }
-        Ok(())
-    }
-}
-
-struct RestoreEngine<'a> {
-    repository_path: &'a Path,
-    target_path: &'a Path,
-}
-
-enum RestoreDescriptor {
-    All,
-    SpecificPath(String),
-}
-
-impl<'a> RestoreEngine<'a> {
-    fn new(repository_path: &'a Path, target_path: &'a Path) -> Self {
-        RestoreEngine {
-            repository_path,
-            target_path,
-        }
-    }
-
-    fn restore_all(&self) -> Result<(), io::Error> {
-        self.restore(RestoreDescriptor::All)
-    }
-
-    fn restore(&self, what: RestoreDescriptor) -> Result<(), io::Error> {
-        self.restore_as_of_version(what, 0)
-    }
-
-    fn restore_as_of_version(&self, what: RestoreDescriptor, version: u64) -> Result<(), io::Error> {
-        let walker = WalkDir::new(self.repository_path);
-        for maybe_entry in walker {
-            match maybe_entry {
-                Ok(entry) => {
-                    if entry.path() != self.repository_path {
-                        self.process_entry(&entry)?;
-                    }
-                }
-                Err(error) => return Err(error.into()),
-            }
-        }
-        Ok(())
-    }
-
-    fn process_entry(&self, entry: &DirEntry) -> Result<(), io::Error> {
-        if entry.file_type().is_dir() {
-            fs::create_dir(self.target_path.join(entry.file_name()))?;
-        }
-        if entry.file_type().is_file() {
-            fs::copy(entry.path(), self.target_path.join(entry.file_name()))?;
-        }
-        Ok(())
-    }
-}
 
 fn main() {}
 
-mod bakare {
-
-    #[cfg(test)]
-    mod should {
-
-        use dir_diff::is_different;
-        use std::fs::File;
-        use std::io::Error;
-        use std::io::Read;
-        use std::io::Write;
-        use std::path::Path;
-        use tempfile::tempdir;
-        use tempfile::TempDir;
-        use BackupEngine;
-        use RestoreDescriptor;
-        use RestoreDescriptor::SpecificPath;
-        use RestoreEngine;
-
-        #[test]
-        fn restore_backed_up_files() -> Result<(), Error> {
-            let source = Source::new()?;
-            let repository = tempdir()?;
-
-            source.write_text_to_file("first", "some contents");
-            source.write_text_to_file("second", "some contents");
-            source.write_text_to_file("third", "some other contents");
-
-            assert_same_after_restore(source.path(), repository.path())
-        }
-
-        #[test]
-        fn restore_older_version_of_file() -> Result<(), Error> {
-            let source = Source::new()?;
-            let repository = tempdir()?;
-            let backup_engine = BackupEngine::new(source.path(), repository.path());
-            let path = "some path";
-            let new_contents = "totally new contents";
-            let restore_target = tempdir()?;
-            let restore_engine = RestoreEngine::new(repository.path(), &restore_target.path());
-            let old_contents = "some old contents";
-
-            source.write_text_to_file(path, old_contents)?;
-            backup_engine.backup()?;
-            let old_version = backup_engine.file_version(path.as_ref());
-
-            source.write_text_to_file(path, new_contents)?;
-            backup_engine.backup()?;
-
-            restore_engine.restore_as_of_version(SpecificPath(path.into()), old_version)?;
-
-            assert_target_file_contents(restore_target.path(), path, old_contents)?;
-            Ok(())
-        }
-
-        // TODO: restore latest version by default
-        // TODO: deduplicate data
-
-        fn assert_target_file_contents(target: &Path, filename: &str, expected_contents: &str) -> Result<(), Error> {
-            let restored_path = target.join(filename);
-            let mut actual_contents = String::new();
-            File::open(restored_path)?.read_to_string(&mut actual_contents)?;
-            assert_eq!(expected_contents, actual_contents);
-            Ok(())
-        }
-
-        fn assert_same_after_restore(source_path: &Path, repository_path: &Path) -> Result<(), Error> {
-            let backup_engine = BackupEngine::new(source_path, repository_path);
-            backup_engine.backup()?;
-
-            let restore_target = tempdir()?;
-            let restore_engine = RestoreEngine::new(repository_path, &restore_target.path());
-            restore_engine.restore_all()?;
-
-            let are_source_and_target_different = is_different(source_path, &restore_target.path()).unwrap();
-            assert!(!are_source_and_target_different);
-            Ok(())
-        }
-
-        struct Source {
-            directory: TempDir,
-        }
-
-        impl Source {
-            fn new() -> Result<Self, Error> {
-                Ok(Self { directory: tempdir()? })
-            }
-
-            fn write_text_to_file(&self, filename: &str, text: &str) -> Result<(), Error> {
-                Ok(File::create(self.directory.path().join(filename))?.write_all(text.as_bytes())?)
-            }
-
-            fn path(&self) -> &Path {
-                self.directory.path()
-            }
-        }
-
-    }
-
-}
diff --git a/src/restore.rs b/src/restore.rs
new file mode 100644
index 0000000..5bc7ac5
--- /dev/null
+++ b/src/restore.rs
@@ -0,0 +1,58 @@
+use std::io;
+use std::path::Path;
+use walkdir::WalkDir;
+use walkdir::DirEntry;
+use std::fs;
+
+pub struct RestoreEngine<'a> {
+    repository_path: &'a Path,
+    target_path: &'a Path,
+}
+
+pub enum RestoreDescriptor {
+    All,
+    SpecificPath(String),
+}
+
+impl<'a> RestoreEngine<'a> {
+    pub fn new(repository_path: &'a Path, target_path: &'a Path) -> Self {
+        RestoreEngine {
+            repository_path,
+            target_path,
+        }
+    }
+
+    pub fn restore_all(&self) -> Result<(), io::Error> {
+        self.restore(RestoreDescriptor::All)
+    }
+
+    fn restore(&self, what: RestoreDescriptor) -> Result<(), io::Error> {
+        self.restore_as_of_version(what, 0)
+    }
+
+    pub fn restore_as_of_version(&self, what: RestoreDescriptor, version: u64) -> Result<(), io::Error> {
+        let walker = WalkDir::new(self.repository_path);
+        for maybe_entry in walker {
+            match maybe_entry {
+                Ok(entry) => {
+                    if entry.path() != self.repository_path {
+                        self.process_entry(&entry)?;
+                    }
+                }
+                Err(error) => return Err(error.into()),
+            }
+        }
+        Ok(())
+    }
+
+    fn process_entry(&self, entry: &DirEntry) -> Result<(), io::Error> {
+        if entry.file_type().is_dir() {
+            fs::create_dir(self.target_path.join(entry.file_name()))?;
+        }
+        if entry.file_type().is_file() {
+            fs::copy(entry.path(), self.target_path.join(entry.file_name()))?;
+        }
+        Ok(())
+    }
+}
+
diff --git a/tests/system_tests.rs b/tests/system_tests.rs
new file mode 100644
index 0000000..26f7b56
--- /dev/null
+++ b/tests/system_tests.rs
@@ -0,0 +1,95 @@
+extern crate bakare;
+extern crate tempfile;
+extern crate dir_diff;
+
+use dir_diff::is_different;
+use std::fs::File;
+use std::io::Error;
+use std::io::Read;
+use std::io::Write;
+use std::path::Path;
+use tempfile::tempdir;
+use tempfile::TempDir;
+use bakare::backup::BackupEngine;
+use bakare::restore::RestoreDescriptor;
+use bakare::restore::RestoreDescriptor::SpecificPath;
+use bakare::restore::RestoreEngine;
+
+#[test]
+fn restore_backed_up_files() -> Result<(), Error> {
+    let source = Source::new()?;
+    let repository = tempdir()?;
+
+    source.write_text_to_file("first", "some contents");
+    source.write_text_to_file("second", "some contents");
+    source.write_text_to_file("third", "some other contents");
+
+    assert_same_after_restore(source.path(), repository.path())
+}
+
+#[test]
+fn restore_older_version_of_file() -> Result<(), Error> {
+    let source = Source::new()?;
+    let repository = tempdir()?;
+    let backup_engine = BackupEngine::new(source.path(), repository.path());
+    let path = "some path";
+    let new_contents = "totally new contents";
+    let restore_target = tempdir()?;
+    let restore_engine = RestoreEngine::new(repository.path(), &restore_target.path());
+    let old_contents = "some old contents";
+
+    source.write_text_to_file(path, old_contents)?;
+    backup_engine.backup()?;
+    let old_version = backup_engine.file_version(path.as_ref());
+
+    source.write_text_to_file(path, new_contents)?;
+    backup_engine.backup()?;
+
+    restore_engine.restore_as_of_version(SpecificPath(path.into()), old_version)?;
+
+    assert_target_file_contents(restore_target.path(), path, old_contents)?;
+    Ok(())
+}
+
+// TODO: restore latest version by default
+// TODO: deduplicate data
+
+fn assert_target_file_contents(target: &Path, filename: &str, expected_contents: &str) -> Result<(), Error> {
+    let restored_path = target.join(filename);
+    let mut actual_contents = String::new();
+    File::open(restored_path)?.read_to_string(&mut actual_contents)?;
+    assert_eq!(expected_contents, actual_contents);
+    Ok(())
+}
+
+fn assert_same_after_restore(source_path: &Path, repository_path: &Path) -> Result<(), Error> {
+    let backup_engine = BackupEngine::new(source_path, repository_path);
+    backup_engine.backup()?;
+
+    let restore_target = tempdir()?;
+    let restore_engine = RestoreEngine::new(repository_path, &restore_target.path());
+    restore_engine.restore_all()?;
+
+    let are_source_and_target_different = is_different(source_path, &restore_target.path()).unwrap();
+    assert!(!are_source_and_target_different);
+    Ok(())
+}
+
+struct Source {
+    directory: TempDir,
+}
+
+impl Source {
+    fn new() -> Result<Self, Error> {
+        Ok(Self { directory: tempdir()? })
+    }
+
+    fn write_text_to_file(&self, filename: &str, text: &str) -> Result<(), Error> {
+        Ok(File::create(self.directory.path().join(filename))?.write_all(text.as_bytes())?)
+    }
+
+    fn path(&self) -> &Path {
+        self.directory.path()
+    }
+}
+