add freelist interface unit tests

Signed-off-by: Thomas Jungblut <[email protected]>

internal/freelist/array.go

@@ -101,6 +101,7 @@ func (f *array) mergeSpans(ids common.Pgids) {
 func NewArrayFreelist() Interface {
 	a := &array{
 		shared: newShared(),
+		ids:    []common.Pgid{},
 	}
 	a.Interface = a
 	return a

internal/freelist/freelist.go

@@ -11,7 +11,7 @@ type ReadWriter interface {
 	// Write writes the freelist into the given page.
 	Write(page *common.Page)
 
-	// EstimatedWritePageSize returns the size of the freelist after serialization in Write.
+	// EstimatedWritePageSize returns the size in bytes of the freelist after serialization in Write.
 	// This should never underestimate the size.
 	EstimatedWritePageSize() int
 }
@@ -46,13 +46,14 @@ type Interface interface {
 	ReleasePendingPages()
 
 	// Free releases a page and its overflow for a given transaction id.
-	// If the page is already free then a panic will occur.
+	// If the page is already free or is one of the meta pages, then a panic will occur.
 	Free(txId common.Txid, p *common.Page)
 
 	// Freed returns whether a given page is in the free list.
 	Freed(pgId common.Pgid) bool
 
 	// Rollback removes the pages from a given pending tx.
+	// Should always be followed by Reload or NoSyncReload from last freelist state.
 	Rollback(txId common.Txid)
 
 	// Copyall copies a list of all free ids and all pending ids in one sorted list.
@@ -65,7 +66,7 @@ type Interface interface {
 	// NoSyncReload reads the freelist from Pgids and filters out pending items.
 	NoSyncReload(pgIds common.Pgids)
 
-	// freePageIds returns the IDs of all free pages.
+	// freePageIds returns the IDs of all free pages. No free pages returns an empty slice.
 	freePageIds() common.Pgids
 
 	// pendingPageIds returns all pending pages by transaction id.