diff --git a/db.go b/db.go
index 710d155..c08f541 100644
--- a/db.go
+++ b/db.go
@@ -219,7 +219,7 @@ func (db *DB) Pos() (Pos, error) {
 		return Pos{}, err
 	}
 
-	return Pos{Generation: generation, Index: index, Offset: fi.Size()}, nil
+	return Pos{Generation: generation, Index: index, Offset: frameAlign(fi.Size(), db.pageSize)}, nil
 }
 
 // Notify returns a channel that closes when the shadow WAL changes.
@@ -764,16 +764,16 @@ func (db *DB) verify() (info syncInfo, err error) {
 
 	// Open shadow WAL to copy append to.
 	info.shadowWALPath, err = db.CurrentShadowWALPath(info.generation)
-	if info.shadowWALPath == "" {
-		info.reason = "no shadow wal"
-		return info, nil
-	} else if err != nil {
+	if err != nil {
 		return info, fmt.Errorf("cannot determine shadow WAL: %w", err)
 	}
 
 	// Determine shadow WAL current size.
 	fi, err = os.Stat(info.shadowWALPath)
-	if err != nil {
+	if os.IsNotExist(err) {
+		info.reason = "no shadow wal"
+		return info, nil
+	} else if err != nil {
 		return info, err
 	}
 	info.shadowWALSize = frameAlign(fi.Size(), db.pageSize)
@@ -781,7 +781,8 @@ func (db *DB) verify() (info syncInfo, err error) {
 	// Truncate shadow WAL if there is a partial page.
 	// Exit if shadow WAL does not contain a full header.
 	if info.shadowWALSize < WALHeaderSize {
-		return info, fmt.Errorf("short shadow wal: %s", info.shadowWALPath)
+		info.reason = "short shadow wal"
+		return info, nil
 	}
 
 	// If shadow WAL is larger than real WAL then the WAL has been truncated
@@ -907,6 +908,7 @@ func (db *DB) copyToShadowWAL(filename string) (newSize int64, err error) {
 	if err != nil {
 		return 0, err
 	}
+	origSize := frameAlign(fi.Size(), db.pageSize)
 
 	// Read shadow WAL header to determine byte order for checksum & salt.
 	hdr := make([]byte, WALHeaderSize)
@@ -928,16 +930,13 @@ func (db *DB) copyToShadowWAL(filename string) (newSize int64, err error) {
 	}
 
 	// Seek to correct position on both files.
-	if _, err := r.Seek(fi.Size(), io.SeekStart); err != nil {
+	if _, err := r.Seek(origSize, io.SeekStart); err != nil {
 		return 0, fmt.Errorf("wal seek: %w", err)
-	} else if _, err := w.Seek(fi.Size(), io.SeekStart); err != nil {
+	} else if _, err := w.Seek(origSize, io.SeekStart); err != nil {
 		return 0, fmt.Errorf("shadow wal seek: %w", err)
 	}
 
-	// TODO: Optimize to use bufio on reader & writer to minimize syscalls.
-
 	// Loop over each page, verify checksum, & copy to writer.
-	origSize := fi.Size()
 	newSize = origSize
 	buf := make([]byte, db.pageSize+WALFrameHeaderSize)
 	for {
@@ -1103,8 +1102,8 @@ func readLastChecksumFrom(f *os.File, pageSize int) (uint32, uint32, error) {
 	offset := int64(WALHeaderChecksumOffset)
 	if fi, err := f.Stat(); err != nil {
 		return 0, 0, err
-	} else if fi.Size() > WALHeaderSize {
-		offset = fi.Size() - int64(pageSize) - WALFrameHeaderSize + WALFrameHeaderChecksumOffset
+	} else if sz := frameAlign(fi.Size(), pageSize); fi.Size() > WALHeaderSize {
+		offset = sz - int64(pageSize) - WALFrameHeaderSize + WALFrameHeaderChecksumOffset
 	}
 
 	// Read big endian checksum.
@@ -1117,8 +1116,19 @@ func readLastChecksumFrom(f *os.File, pageSize int) (uint32, uint32, error) {
 	return binary.BigEndian.Uint32(b[0:]), binary.BigEndian.Uint32(b[4:]), nil
 }
 
-// checkpoint performs a checkpoint on the WAL file.
+// Checkpoint performs a checkpoint on the WAL file.
+func (db *DB) Checkpoint(mode string) (err error) {
+	db.mu.Lock()
+	defer db.mu.Unlock()
+	return db.checkpoint(mode)
+}
+
 func (db *DB) checkpoint(mode string) (err error) {
+	// Ignore if there is no underlying database.
+	if db.db == nil {
+		return nil
+	}
+
 	// Track checkpoint metrics.
 	t := time.Now()
 	defer func() {
diff --git a/db_test.go b/db_test.go
index ec0cf7c..688c413 100644
--- a/db_test.go
+++ b/db_test.go
@@ -2,6 +2,7 @@ package litestream_test
 
 import (
 	"database/sql"
+	"io/ioutil"
 	"os"
 	"path/filepath"
 	"testing"
@@ -193,39 +194,327 @@ func TestDB_Sync(t *testing.T) {
 		}
 	})
 
-	// Ensure a WAL file is created if one does not already exist.
-	t.Run("NoWAL", func(t *testing.T) {
-		t.Skip()
-	})
-
 	// Ensure DB can keep in sync across multiple Sync() invocations.
 	t.Run("MultiSync", func(t *testing.T) {
-		t.Skip()
+		db, sqldb := MustOpenDBs(t)
+		defer MustCloseDBs(t, db, sqldb)
+
+		// Execute a query to force a write to the WAL.
+		if _, err := sqldb.Exec(`CREATE TABLE foo (bar TEXT);`); err != nil {
+			t.Fatal(err)
+		}
+
+		// Perform initial sync & grab initial position.
+		if err := db.Sync(); err != nil {
+			t.Fatal(err)
+		}
+
+		pos0, err := db.Pos()
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		// Insert into table.
+		if _, err := sqldb.Exec(`INSERT INTO foo (bar) VALUES ('baz');`); err != nil {
+			t.Fatal(err)
+		}
+
+		// Sync to ensure position moves forward one page.
+		if err := db.Sync(); err != nil {
+			t.Fatal(err)
+		} else if pos1, err := db.Pos(); err != nil {
+			t.Fatal(err)
+		} else if pos0.Generation != pos1.Generation {
+			t.Fatal("expected the same generation")
+		} else if got, want := pos1.Index, pos0.Index; got != want {
+			t.Fatalf("Index=%v, want %v", got, want)
+		} else if got, want := pos1.Offset, pos0.Offset+4096+litestream.WALFrameHeaderSize; got != want {
+			t.Fatalf("Offset=%v, want %v", got, want)
+		}
+	})
+
+	// Ensure a WAL file is created if one does not already exist.
+	t.Run("NoWAL", func(t *testing.T) {
+		db, sqldb := MustOpenDBs(t)
+		defer MustCloseDBs(t, db, sqldb)
+
+		// Issue initial sync and truncate WAL.
+		if err := db.Sync(); err != nil {
+			t.Fatal(err)
+		}
+
+		// Obtain initial position.
+		pos0, err := db.Pos()
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		// Checkpoint & fully close which should close WAL file.
+		if err := db.Checkpoint(litestream.CheckpointModeTruncate); err != nil {
+			t.Fatal(err)
+		} else if err := db.Close(); err != nil {
+			t.Fatal(err)
+		} else if err := sqldb.Close(); err != nil {
+			t.Fatal(err)
+		}
+
+		// Verify WAL does not exist.
+		if _, err := os.Stat(db.WALPath()); !os.IsNotExist(err) {
+			t.Fatal(err)
+		}
+
+		// Reopen the managed database.
+		db = MustOpenDBAt(t, db.Path())
+		defer MustCloseDB(t, db)
+
+		// Re-sync and ensure new generation has been created.
+		if err := db.Sync(); err != nil {
+			t.Fatal(err)
+		}
+
+		// Obtain initial position.
+		if pos1, err := db.Pos(); err != nil {
+			t.Fatal(err)
+		} else if pos0.Generation == pos1.Generation {
+			t.Fatal("expected new generation after truncation")
+		}
 	})
 
 	// Ensure DB can start new generation if it detects it cannot verify last position.
-	t.Run("NewGeneration", func(t *testing.T) {
-		t.Skip()
+	t.Run("OverwritePrevPosition", func(t *testing.T) {
+		db, sqldb := MustOpenDBs(t)
+		defer MustCloseDBs(t, db, sqldb)
+
+		// Execute a query to force a write to the WAL.
+		if _, err := sqldb.Exec(`CREATE TABLE foo (bar TEXT);`); err != nil {
+			t.Fatal(err)
+		}
+
+		// Issue initial sync and truncate WAL.
+		if err := db.Sync(); err != nil {
+			t.Fatal(err)
+		}
+
+		// Obtain initial position.
+		pos0, err := db.Pos()
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		// Fully close which should close WAL file.
+		if err := db.Close(); err != nil {
+			t.Fatal(err)
+		} else if err := sqldb.Close(); err != nil {
+			t.Fatal(err)
+		}
+
+		// Verify WAL does not exist.
+		if _, err := os.Stat(db.WALPath()); !os.IsNotExist(err) {
+			t.Fatal(err)
+		}
+
+		// Insert into table multiple times to move past old offset
+		sqldb = MustOpenSQLDB(t, db.Path())
+		defer MustCloseSQLDB(t, sqldb)
+		for i := 0; i < 100; i++ {
+			if _, err := sqldb.Exec(`INSERT INTO foo (bar) VALUES ('baz');`); err != nil {
+				t.Fatal(err)
+			}
+		}
+
+		// Reopen the managed database.
+		db = MustOpenDBAt(t, db.Path())
+		defer MustCloseDB(t, db)
+
+		// Re-sync and ensure new generation has been created.
+		if err := db.Sync(); err != nil {
+			t.Fatal(err)
+		}
+
+		// Obtain initial position.
+		if pos1, err := db.Pos(); err != nil {
+			t.Fatal(err)
+		} else if pos0.Generation == pos1.Generation {
+			t.Fatal("expected new generation after truncation")
+		}
+	})
+
+	// Ensure DB can handle a mismatched header-only and start new generation.
+	t.Run("WALHeaderMismatch", func(t *testing.T) {
+		db, sqldb := MustOpenDBs(t)
+		defer MustCloseDBs(t, db, sqldb)
+
+		// Execute a query to force a write to the WAL and then sync.
+		if _, err := sqldb.Exec(`CREATE TABLE foo (bar TEXT);`); err != nil {
+			t.Fatal(err)
+		} else if err := db.Sync(); err != nil {
+			t.Fatal(err)
+		}
+
+		// Grab initial position & close.
+		pos0, err := db.Pos()
+		if err != nil {
+			t.Fatal(err)
+		} else if err := db.Close(); err != nil {
+			t.Fatal(err)
+		}
+
+		// Read existing file, update header checksum, and write back only header
+		// to simulate a header with a mismatched checksum.
+		shadowWALPath := db.ShadowWALPath(pos0.Generation, pos0.Index)
+		if buf, err := ioutil.ReadFile(shadowWALPath); err != nil {
+			t.Fatal(err)
+		} else if ioutil.WriteFile(shadowWALPath, append(buf[:litestream.WALHeaderSize-8], 0, 0, 0, 0, 0, 0, 0, 0), 0600); err != nil {
+			t.Fatal(err)
+		}
+
+		// Reopen managed database & ensure sync will still work.
+		db = MustOpenDBAt(t, db.Path())
+		defer MustCloseDB(t, db)
+		if err := db.Sync(); err != nil {
+			t.Fatal(err)
+		}
+
+		// Verify a new generation was started.
+		if pos1, err := db.Pos(); err != nil {
+			t.Fatal(err)
+		} else if pos0.Generation == pos1.Generation {
+			t.Fatal("expected new generation")
+		}
 	})
 
 	// Ensure DB can handle partial shadow WAL header write.
 	t.Run("PartialShadowWALHeader", func(t *testing.T) {
-		t.Skip()
+		db, sqldb := MustOpenDBs(t)
+		defer MustCloseDBs(t, db, sqldb)
+
+		// Execute a query to force a write to the WAL and then sync.
+		if _, err := sqldb.Exec(`CREATE TABLE foo (bar TEXT);`); err != nil {
+			t.Fatal(err)
+		} else if err := db.Sync(); err != nil {
+			t.Fatal(err)
+		}
+
+		pos0, err := db.Pos()
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		// Close & truncate shadow WAL to simulate a partial header write.
+		if err := db.Close(); err != nil {
+			t.Fatal(err)
+		} else if err := os.Truncate(db.ShadowWALPath(pos0.Generation, pos0.Index), litestream.WALHeaderSize-1); err != nil {
+			t.Fatal(err)
+		}
+
+		// Reopen managed database & ensure sync will still work.
+		db = MustOpenDBAt(t, db.Path())
+		defer MustCloseDB(t, db)
+		if err := db.Sync(); err != nil {
+			t.Fatal(err)
+		}
+
+		// Verify a new generation was started.
+		if pos1, err := db.Pos(); err != nil {
+			t.Fatal(err)
+		} else if pos0.Generation == pos1.Generation {
+			t.Fatal("expected new generation")
+		}
 	})
 
 	// Ensure DB can handle partial shadow WAL writes.
 	t.Run("PartialShadowWALFrame", func(t *testing.T) {
-		t.Skip()
+		db, sqldb := MustOpenDBs(t)
+		defer MustCloseDBs(t, db, sqldb)
+
+		// Execute a query to force a write to the WAL and then sync.
+		if _, err := sqldb.Exec(`CREATE TABLE foo (bar TEXT);`); err != nil {
+			t.Fatal(err)
+		} else if err := db.Sync(); err != nil {
+			t.Fatal(err)
+		}
+
+		pos0, err := db.Pos()
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		// Obtain current shadow WAL size.
+		fi, err := os.Stat(db.ShadowWALPath(pos0.Generation, pos0.Index))
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		// Close & truncate shadow WAL to simulate a partial frame write.
+		if err := db.Close(); err != nil {
+			t.Fatal(err)
+		} else if err := os.Truncate(db.ShadowWALPath(pos0.Generation, pos0.Index), fi.Size()-1); err != nil {
+			t.Fatal(err)
+		}
+
+		// Reopen managed database & ensure sync will still work.
+		db = MustOpenDBAt(t, db.Path())
+		defer MustCloseDB(t, db)
+		if err := db.Sync(); err != nil {
+			t.Fatal(err)
+		}
+
+		// Verify same generation is kept.
+		if pos1, err := db.Pos(); err != nil {
+			t.Fatal(err)
+		} else if got, want := pos1, pos0; got != want {
+			t.Fatalf("Pos()=%s want %s", got, want)
+		}
+
+		// Ensure shadow WAL has recovered.
+		if fi0, err := os.Stat(db.ShadowWALPath(pos0.Generation, pos0.Index)); err != nil {
+			t.Fatal(err)
+		} else if got, want := fi0.Size(), fi.Size(); got != want {
+			t.Fatalf("Size()=%v, want %v", got, want)
+		}
 	})
 
 	// Ensure DB can handle a generation directory with a missing shadow WAL.
 	t.Run("NoShadowWAL", func(t *testing.T) {
-		t.Skip()
-	})
+		db, sqldb := MustOpenDBs(t)
+		defer MustCloseDBs(t, db, sqldb)
 
-	// Ensure DB can handle a mismatched header-only and start new generation.
-	t.Run("MismatchHeaderOnly", func(t *testing.T) {
-		t.Skip()
+		// Execute a query to force a write to the WAL and then sync.
+		if _, err := sqldb.Exec(`CREATE TABLE foo (bar TEXT);`); err != nil {
+			t.Fatal(err)
+		} else if err := db.Sync(); err != nil {
+			t.Fatal(err)
+		}
+
+		pos0, err := db.Pos()
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		// Close & delete shadow WAL to simulate dir created but not WAL.
+		if err := db.Close(); err != nil {
+			t.Fatal(err)
+		} else if err := os.Remove(db.ShadowWALPath(pos0.Generation, pos0.Index)); err != nil {
+			t.Fatal(err)
+		}
+
+		// Reopen managed database & ensure sync will still work.
+		db = MustOpenDBAt(t, db.Path())
+		defer MustCloseDB(t, db)
+		if err := db.Sync(); err != nil {
+			t.Fatal(err)
+		}
+
+		// Verify new generation created but index/offset the same.
+		if pos1, err := db.Pos(); err != nil {
+			t.Fatal(err)
+		} else if pos0.Generation == pos1.Generation {
+			t.Fatal("expected new generation")
+		} else if got, want := pos1.Index, pos0.Index; got != want {
+			t.Fatalf("Index=%v want %v", got, want)
+		} else if got, want := pos1.Offset, pos0.Offset; got != want {
+			t.Fatalf("Offset=%v want %v", got, want)
+		}
 	})
 
 	// Ensure DB checkpoints after minimum number of pages.
@@ -258,10 +547,14 @@ func MustCloseDBs(tb testing.TB, db *litestream.DB, sqldb *sql.DB) {
 
 // MustOpenDB returns a new instance of a DB.
 func MustOpenDB(tb testing.TB) *litestream.DB {
-	tb.Helper()
-
 	dir := tb.TempDir()
-	db := litestream.NewDB(filepath.Join(dir, "db"))
+	return MustOpenDBAt(tb, filepath.Join(dir, "db"))
+}
+
+// MustOpenDBAt returns a new instance of a DB for a given path.
+func MustOpenDBAt(tb testing.TB, path string) *litestream.DB {
+	tb.Helper()
+	db := litestream.NewDB(path)
 	db.MonitorInterval = 0 // disable background goroutine
 	if err := db.Open(); err != nil {
 		tb.Fatal(err)