[storage] Add clear() to WriteAheadLog #143 (#144)

* Update write_ahead_log.rs

* Update write_ahead_log.rs

.github/workflows/pr.yaml

@@ -44,7 +44,7 @@ jobs:
       - uses: actions/checkout@v3
       - uses: taiki-e/install-action@cargo-llvm-cov
       - run: rustup component add llvm-tools-preview
-      - run: cargo llvm-cov --fail-uncovered-regions 62 --fail-uncovered-functions 0 --fail-uncovered-lines 1
+      - run: cargo llvm-cov --fail-uncovered-regions 63 --fail-uncovered-functions 0 --fail-uncovered-lines 1
 
   test:
     runs-on: ubuntu-latest

src/storage/write_ahead_log.rs

@@ -12,6 +12,10 @@ pub(crate) struct WriteAheadLog {
 
 #[allow(dead_code)]
 impl WriteAheadLog {
+    pub(crate) fn clear(&mut self) -> Result<(), DbError> {
+        Ok(self.file.set_len(0)?)
+    }
+
     pub(crate) fn insert(&mut self, record: WriteAheadLogRecord) -> Result<(), DbError> {
         self.file.write_all(&record.position.serialize())?;
         self.file
@@ -75,6 +79,22 @@ mod tests {
         WriteAheadLog::try_from(test_file.file_name().clone()).unwrap();
     }
 
+    #[test]
+    fn clear() {
+        let test_file = TestFile::from("./write_ahead_log-clear.agdb");
+
+        let mut wal = WriteAheadLog::try_from(test_file.file_name().clone()).unwrap();
+        let record = WriteAheadLogRecord {
+            position: 1,
+            bytes: vec![1_u8; 5],
+        };
+
+        wal.insert(record).unwrap();
+        wal.clear().unwrap();
+
+        assert_eq!(wal.records(), Ok(vec![]));
+    }
+
     #[test]
     fn insert() {
         let test_file = TestFile::from("./write_ahead_log-insert.agdb");