diff --git a/libraries/persistent_store/src/fragment.rs b/libraries/persistent_store/src/fragment.rs
index 73b6d29..9aec377 100644
--- a/libraries/persistent_store/src/fragment.rs
+++ b/libraries/persistent_store/src/fragment.rs
@@ -177,3 +177,168 @@ fn get_handles(store: &Store<impl Storage>, keys: &impl Keys) -> StoreResult<Vec
     }
     Ok(result)
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::test::MINIMAL;
+
+    #[test]
+    fn read_empty_entry() {
+        let store = MINIMAL.new_store();
+        assert_eq!(read(&store, &(0..4)), Ok(None));
+    }
+
+    #[test]
+    fn read_single_chunk() {
+        let mut store = MINIMAL.new_store();
+        let value = b"hello".to_vec();
+        assert_eq!(store.insert(0, &value), Ok(()));
+        assert_eq!(read(&store, &(0..4)), Ok(Some(value)));
+    }
+
+    #[test]
+    fn read_multiple_chunks() {
+        let mut store = MINIMAL.new_store();
+        let value: Vec<_> = (0..60).collect();
+        assert_eq!(store.insert(0, &value[..52]), Ok(()));
+        assert_eq!(store.insert(1, &value[52..]), Ok(()));
+        assert_eq!(read(&store, &(0..4)), Ok(Some(value)));
+    }
+
+    #[test]
+    fn read_range_first_chunk() {
+        let mut store = MINIMAL.new_store();
+        let value: Vec<_> = (0..60).collect();
+        assert_eq!(store.insert(0, &value[..52]), Ok(()));
+        assert_eq!(store.insert(1, &value[52..]), Ok(()));
+        assert_eq!(
+            read_range(&store, &(0..4), 0..10),
+            Ok(Some((0..10).collect()))
+        );
+        assert_eq!(
+            read_range(&store, &(0..4), 10..20),
+            Ok(Some((10..20).collect()))
+        );
+        assert_eq!(
+            read_range(&store, &(0..4), 40..52),
+            Ok(Some((40..52).collect()))
+        );
+    }
+
+    #[test]
+    fn read_range_second_chunk() {
+        let mut store = MINIMAL.new_store();
+        let value: Vec<_> = (0..60).collect();
+        assert_eq!(store.insert(0, &value[..52]), Ok(()));
+        assert_eq!(store.insert(1, &value[52..]), Ok(()));
+        assert_eq!(read_range(&store, &(0..4), 52..53), Ok(Some(vec![52])));
+        assert_eq!(read_range(&store, &(0..4), 53..54), Ok(Some(vec![53])));
+        assert_eq!(read_range(&store, &(0..4), 59..60), Ok(Some(vec![59])));
+    }
+
+    #[test]
+    fn read_range_both_chunks() {
+        let mut store = MINIMAL.new_store();
+        let value: Vec<_> = (0..60).collect();
+        assert_eq!(store.insert(0, &value[..52]), Ok(()));
+        assert_eq!(store.insert(1, &value[52..]), Ok(()));
+        assert_eq!(
+            read_range(&store, &(0..4), 40..60),
+            Ok(Some((40..60).collect()))
+        );
+        assert_eq!(
+            read_range(&store, &(0..4), 0..60),
+            Ok(Some((0..60).collect()))
+        );
+    }
+
+    #[test]
+    fn read_range_outside() {
+        let mut store = MINIMAL.new_store();
+        let value: Vec<_> = (0..60).collect();
+        assert_eq!(store.insert(0, &value[..52]), Ok(()));
+        assert_eq!(store.insert(1, &value[52..]), Ok(()));
+        assert_eq!(
+            read_range(&store, &(0..4), 40..100),
+            Ok(Some((40..60).collect()))
+        );
+        assert_eq!(read_range(&store, &(0..4), 60..100), Ok(Some(vec![])));
+    }
+
+    #[test]
+    fn write_single_chunk() {
+        let mut store = MINIMAL.new_store();
+        let value = b"hello".to_vec();
+        assert_eq!(write(&mut store, &(0..4), &value), Ok(()));
+        assert_eq!(store.find(0), Ok(Some(value)));
+        assert_eq!(store.find(1), Ok(None));
+        assert_eq!(store.find(2), Ok(None));
+        assert_eq!(store.find(3), Ok(None));
+    }
+
+    #[test]
+    fn write_multiple_chunks() {
+        let mut store = MINIMAL.new_store();
+        let value: Vec<_> = (0..60).collect();
+        assert_eq!(write(&mut store, &(0..4), &value), Ok(()));
+        assert_eq!(store.find(0), Ok(Some((0..52).collect())));
+        assert_eq!(store.find(1), Ok(Some((52..60).collect())));
+        assert_eq!(store.find(2), Ok(None));
+        assert_eq!(store.find(3), Ok(None));
+    }
+
+    #[test]
+    fn overwrite_less_chunks() {
+        let mut store = MINIMAL.new_store();
+        let value: Vec<_> = (0..60).collect();
+        assert_eq!(store.insert(0, &value[..52]), Ok(()));
+        assert_eq!(store.insert(1, &value[52..]), Ok(()));
+        let value: Vec<_> = (42..69).collect();
+        assert_eq!(write(&mut store, &(0..4), &value), Ok(()));
+        assert_eq!(store.find(0), Ok(Some((42..69).collect())));
+        assert_eq!(store.find(1), Ok(None));
+        assert_eq!(store.find(2), Ok(None));
+        assert_eq!(store.find(3), Ok(None));
+    }
+
+    #[test]
+    fn overwrite_needed_chunks() {
+        let mut store = MINIMAL.new_store();
+        let mut value: Vec<_> = (0..60).collect();
+        assert_eq!(store.insert(0, &value[..52]), Ok(()));
+        assert_eq!(store.insert(1, &value[52..]), Ok(()));
+        // Current lifetime is 2 words of overhead (2 insert) and 60 bytes of data.
+        let mut lifetime = 2 + 60 / 4;
+        assert_eq!(store.lifetime().unwrap().used(), lifetime);
+        // Update the value.
+        value.extend(60..80);
+        assert_eq!(write(&mut store, &(0..4), &value), Ok(()));
+        // Added lifetime is 1 word of overhead (1 insert) and (80 - 52) bytes of data.
+        lifetime += 1 + (80 - 52) / 4;
+        assert_eq!(store.lifetime().unwrap().used(), lifetime);
+    }
+
+    #[test]
+    fn delete_empty() {
+        let mut store = MINIMAL.new_store();
+        assert_eq!(delete(&mut store, &(0..4)), Ok(()));
+        assert_eq!(store.find(0), Ok(None));
+        assert_eq!(store.find(1), Ok(None));
+        assert_eq!(store.find(2), Ok(None));
+        assert_eq!(store.find(3), Ok(None));
+    }
+
+    #[test]
+    fn delete_chunks() {
+        let mut store = MINIMAL.new_store();
+        let value: Vec<_> = (0..60).collect();
+        assert_eq!(store.insert(0, &value[..52]), Ok(()));
+        assert_eq!(store.insert(1, &value[52..]), Ok(()));
+        assert_eq!(delete(&mut store, &(0..4)), Ok(()));
+        assert_eq!(store.find(0), Ok(None));
+        assert_eq!(store.find(1), Ok(None));
+        assert_eq!(store.find(2), Ok(None));
+        assert_eq!(store.find(3), Ok(None));
+    }
+}
diff --git a/libraries/persistent_store/src/lib.rs b/libraries/persistent_store/src/lib.rs
index 41acbaf..a8adc2b 100644
--- a/libraries/persistent_store/src/lib.rs
+++ b/libraries/persistent_store/src/lib.rs
@@ -1,4 +1,4 @@
-// Copyright 2019-2020 Google LLC
+// Copyright 2019-2021 Google LLC
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -359,6 +359,8 @@ pub mod fragment;
 mod model;
 mod storage;
 mod store;
+#[cfg(test)]
+mod test;
 
 #[cfg(feature = "std")]
 pub use self::buffer::{BufferCorruptFunction, BufferOptions, BufferStorage};
diff --git a/libraries/persistent_store/src/store.rs b/libraries/persistent_store/src/store.rs
index 2630950..f19f463 100644
--- a/libraries/persistent_store/src/store.rs
+++ b/libraries/persistent_store/src/store.rs
@@ -1301,71 +1301,15 @@ fn is_write_needed(source: &[u8], target: &[u8]) -> StoreResult<bool> {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::BufferOptions;
-
-    #[derive(Clone)]
-    struct Config {
-        word_size: usize,
-        page_size: usize,
-        num_pages: usize,
-        max_word_writes: usize,
-        max_page_erases: usize,
-    }
-
-    impl Config {
-        fn new_driver(&self) -> StoreDriverOff {
-            let options = BufferOptions {
-                word_size: self.word_size,
-                page_size: self.page_size,
-                max_word_writes: self.max_word_writes,
-                max_page_erases: self.max_page_erases,
-                strict_mode: true,
-            };
-            StoreDriverOff::new(options, self.num_pages)
-        }
-    }
-
-    const MINIMAL: Config = Config {
-        word_size: 4,
-        page_size: 64,
-        num_pages: 5,
-        max_word_writes: 2,
-        max_page_erases: 9,
-    };
-
-    const NORDIC: Config = Config {
-        word_size: 4,
-        page_size: 0x1000,
-        num_pages: 20,
-        max_word_writes: 2,
-        max_page_erases: 10000,
-    };
-
-    const TITAN: Config = Config {
-        word_size: 4,
-        page_size: 0x800,
-        num_pages: 10,
-        max_word_writes: 2,
-        max_page_erases: 10000,
-    };
+    use crate::test::MINIMAL;
 
     #[test]
-    fn nordic_capacity() {
-        let driver = NORDIC.new_driver().power_on().unwrap();
-        assert_eq!(driver.model().capacity().total, 19123);
-    }
-
-    #[test]
-    fn titan_capacity() {
-        let driver = TITAN.new_driver().power_on().unwrap();
-        assert_eq!(driver.model().capacity().total, 4315);
-    }
-
-    #[test]
-    fn minimal_virt_page_size() {
-        // Make sure a virtual page has 14 words. We use this property in the other tests below to
-        // know whether entries are spanning, starting, and ending pages.
-        assert_eq!(MINIMAL.new_driver().model().format().virt_page_size(), 14);
+    fn is_write_needed_ok() {
+        assert_eq!(is_write_needed(&[], &[]), Ok(false));
+        assert_eq!(is_write_needed(&[0], &[0]), Ok(false));
+        assert_eq!(is_write_needed(&[0], &[1]), Err(StoreError::InvalidStorage));
+        assert_eq!(is_write_needed(&[1], &[0]), Ok(true));
+        assert_eq!(is_write_needed(&[1], &[1]), Ok(false));
     }
 
     #[test]
diff --git a/libraries/persistent_store/tests/config.rs b/libraries/persistent_store/src/test.rs
similarity index 60%
rename from libraries/persistent_store/tests/config.rs
rename to libraries/persistent_store/src/test.rs
index 8812743..2d20574 100644
--- a/libraries/persistent_store/tests/config.rs
+++ b/libraries/persistent_store/src/test.rs
@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-use persistent_store::{BufferOptions, BufferStorage, Store, StoreDriverOff};
+use crate::{BufferOptions, BufferStorage, Store, StoreDriverOff};
 
 #[derive(Clone)]
 pub struct Config {
@@ -47,3 +47,38 @@ pub const MINIMAL: Config = Config {
     max_word_writes: 2,
     max_page_erases: 9,
 };
+
+const NORDIC: Config = Config {
+    word_size: 4,
+    page_size: 0x1000,
+    num_pages: 20,
+    max_word_writes: 2,
+    max_page_erases: 10000,
+};
+
+const TITAN: Config = Config {
+    word_size: 4,
+    page_size: 0x800,
+    num_pages: 10,
+    max_word_writes: 2,
+    max_page_erases: 10000,
+};
+
+#[test]
+fn nordic_capacity() {
+    let driver = NORDIC.new_driver().power_on().unwrap();
+    assert_eq!(driver.model().capacity().total, 19123);
+}
+
+#[test]
+fn titan_capacity() {
+    let driver = TITAN.new_driver().power_on().unwrap();
+    assert_eq!(driver.model().capacity().total, 4315);
+}
+
+#[test]
+fn minimal_virt_page_size() {
+    // Make sure a virtual page has 14 words. We use this property in the other tests below to
+    // know whether entries are spanning, starting, and ending pages.
+    assert_eq!(MINIMAL.new_driver().model().format().virt_page_size(), 14);
+}
diff --git a/libraries/persistent_store/tests/fragment.rs b/libraries/persistent_store/tests/fragment.rs
deleted file mode 100644
index fd045bc..0000000
--- a/libraries/persistent_store/tests/fragment.rs
+++ /dev/null
@@ -1,188 +0,0 @@
-// Copyright 2021 Google LLC
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//      http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-use persistent_store::fragment;
-
-mod config;
-
-#[test]
-fn read_empty_entry() {
-    let store = config::MINIMAL.new_store();
-    assert_eq!(fragment::read(&store, &(0..4)), Ok(None));
-}
-
-#[test]
-fn read_single_chunk() {
-    let mut store = config::MINIMAL.new_store();
-    let value = b"hello".to_vec();
-    assert_eq!(store.insert(0, &value), Ok(()));
-    assert_eq!(fragment::read(&store, &(0..4)), Ok(Some(value)));
-}
-
-#[test]
-fn read_multiple_chunks() {
-    let mut store = config::MINIMAL.new_store();
-    let value: Vec<_> = (0..60).collect();
-    assert_eq!(store.insert(0, &value[..52]), Ok(()));
-    assert_eq!(store.insert(1, &value[52..]), Ok(()));
-    assert_eq!(fragment::read(&store, &(0..4)), Ok(Some(value)));
-}
-
-#[test]
-fn read_range_first_chunk() {
-    let mut store = config::MINIMAL.new_store();
-    let value: Vec<_> = (0..60).collect();
-    assert_eq!(store.insert(0, &value[..52]), Ok(()));
-    assert_eq!(store.insert(1, &value[52..]), Ok(()));
-    assert_eq!(
-        fragment::read_range(&store, &(0..4), 0..10),
-        Ok(Some((0..10).collect()))
-    );
-    assert_eq!(
-        fragment::read_range(&store, &(0..4), 10..20),
-        Ok(Some((10..20).collect()))
-    );
-    assert_eq!(
-        fragment::read_range(&store, &(0..4), 40..52),
-        Ok(Some((40..52).collect()))
-    );
-}
-
-#[test]
-fn read_range_second_chunk() {
-    let mut store = config::MINIMAL.new_store();
-    let value: Vec<_> = (0..60).collect();
-    assert_eq!(store.insert(0, &value[..52]), Ok(()));
-    assert_eq!(store.insert(1, &value[52..]), Ok(()));
-    assert_eq!(
-        fragment::read_range(&store, &(0..4), 52..53),
-        Ok(Some(vec![52]))
-    );
-    assert_eq!(
-        fragment::read_range(&store, &(0..4), 53..54),
-        Ok(Some(vec![53]))
-    );
-    assert_eq!(
-        fragment::read_range(&store, &(0..4), 59..60),
-        Ok(Some(vec![59]))
-    );
-}
-
-#[test]
-fn read_range_both_chunks() {
-    let mut store = config::MINIMAL.new_store();
-    let value: Vec<_> = (0..60).collect();
-    assert_eq!(store.insert(0, &value[..52]), Ok(()));
-    assert_eq!(store.insert(1, &value[52..]), Ok(()));
-    assert_eq!(
-        fragment::read_range(&store, &(0..4), 40..60),
-        Ok(Some((40..60).collect()))
-    );
-    assert_eq!(
-        fragment::read_range(&store, &(0..4), 0..60),
-        Ok(Some((0..60).collect()))
-    );
-}
-
-#[test]
-fn read_range_outside() {
-    let mut store = config::MINIMAL.new_store();
-    let value: Vec<_> = (0..60).collect();
-    assert_eq!(store.insert(0, &value[..52]), Ok(()));
-    assert_eq!(store.insert(1, &value[52..]), Ok(()));
-    assert_eq!(
-        fragment::read_range(&store, &(0..4), 40..100),
-        Ok(Some((40..60).collect()))
-    );
-    assert_eq!(
-        fragment::read_range(&store, &(0..4), 60..100),
-        Ok(Some(vec![]))
-    );
-}
-
-#[test]
-fn write_single_chunk() {
-    let mut store = config::MINIMAL.new_store();
-    let value = b"hello".to_vec();
-    assert_eq!(fragment::write(&mut store, &(0..4), &value), Ok(()));
-    assert_eq!(store.find(0), Ok(Some(value)));
-    assert_eq!(store.find(1), Ok(None));
-    assert_eq!(store.find(2), Ok(None));
-    assert_eq!(store.find(3), Ok(None));
-}
-
-#[test]
-fn write_multiple_chunks() {
-    let mut store = config::MINIMAL.new_store();
-    let value: Vec<_> = (0..60).collect();
-    assert_eq!(fragment::write(&mut store, &(0..4), &value), Ok(()));
-    assert_eq!(store.find(0), Ok(Some((0..52).collect())));
-    assert_eq!(store.find(1), Ok(Some((52..60).collect())));
-    assert_eq!(store.find(2), Ok(None));
-    assert_eq!(store.find(3), Ok(None));
-}
-
-#[test]
-fn overwrite_less_chunks() {
-    let mut store = config::MINIMAL.new_store();
-    let value: Vec<_> = (0..60).collect();
-    assert_eq!(store.insert(0, &value[..52]), Ok(()));
-    assert_eq!(store.insert(1, &value[52..]), Ok(()));
-    let value: Vec<_> = (42..69).collect();
-    assert_eq!(fragment::write(&mut store, &(0..4), &value), Ok(()));
-    assert_eq!(store.find(0), Ok(Some((42..69).collect())));
-    assert_eq!(store.find(1), Ok(None));
-    assert_eq!(store.find(2), Ok(None));
-    assert_eq!(store.find(3), Ok(None));
-}
-
-#[test]
-fn overwrite_needed_chunks() {
-    let mut store = config::MINIMAL.new_store();
-    let mut value: Vec<_> = (0..60).collect();
-    assert_eq!(store.insert(0, &value[..52]), Ok(()));
-    assert_eq!(store.insert(1, &value[52..]), Ok(()));
-    // Current lifetime is 2 words of overhead (2 insert) and 60 bytes of data.
-    let mut lifetime = 2 + 60 / 4;
-    assert_eq!(store.lifetime().unwrap().used(), lifetime);
-    // Update the value.
-    value.extend(60..80);
-    assert_eq!(fragment::write(&mut store, &(0..4), &value), Ok(()));
-    // Added lifetime is 1 word of overhead (1 insert) and (80 - 52) bytes of data.
-    lifetime += 1 + (80 - 52) / 4;
-    assert_eq!(store.lifetime().unwrap().used(), lifetime);
-}
-
-#[test]
-fn delete_empty() {
-    let mut store = config::MINIMAL.new_store();
-    assert_eq!(fragment::delete(&mut store, &(0..4)), Ok(()));
-    assert_eq!(store.find(0), Ok(None));
-    assert_eq!(store.find(1), Ok(None));
-    assert_eq!(store.find(2), Ok(None));
-    assert_eq!(store.find(3), Ok(None));
-}
-
-#[test]
-fn delete_chunks() {
-    let mut store = config::MINIMAL.new_store();
-    let value: Vec<_> = (0..60).collect();
-    assert_eq!(store.insert(0, &value[..52]), Ok(()));
-    assert_eq!(store.insert(1, &value[52..]), Ok(()));
-    assert_eq!(fragment::delete(&mut store, &(0..4)), Ok(()));
-    assert_eq!(store.find(0), Ok(None));
-    assert_eq!(store.find(1), Ok(None));
-    assert_eq!(store.find(2), Ok(None));
-    assert_eq!(store.find(3), Ok(None));
-}