Add db/empty command for asserting that a table is empty

Quite often test cases need to assert that a table has been cleaned up.
To avoid the unnecessary empty table file, add a command for asserting
this.

Signed-off-by: Jussi Maki <[email protected]>

Author: joamaki

any_table.go

@@ -15,6 +15,11 @@ type AnyTable struct {
 	Meta TableMeta
 }
 
+func (t AnyTable) NumObjects(txn ReadTxn) int {
+	indexTxn := txn.getTxn().mustIndexReadTxn(t.Meta, PrimaryIndexPos)
+	return indexTxn.Len()
+}
+
 func (t AnyTable) All(txn ReadTxn) iter.Seq2[any, Revision] {
 	all, _ := t.AllWatch(txn)
 	return all

script.go

@@ -28,6 +28,7 @@ func ScriptCommands(db *DB) hive.ScriptCmdsOut {
 		"db":             DBCmd(db),
 		"db/show":        ShowCmd(db),
 		"db/cmp":         CompareCmd(db),
+		"db/empty":       EmptyCmd(db),
 		"db/insert":      InsertCmd(db),
 		"db/delete":      DeleteCmd(db),
 		"db/get":         GetCmd(db),
@@ -168,8 +169,6 @@ func ShowCmd(db *DB) script.Cmd {
 				fs.StringP("format", "f", "table", "Format to write in (table, yaml or json)")
 			},
 			Detail: []string{
-				"Show the contents of a table.",
-				"",
 				"The contents are written to stdout, but can be written to",
 				"a file instead with the -o flag.",
 				"",
@@ -354,6 +353,28 @@ func CompareCmd(db *DB) script.Cmd {
 		})
 }
 
+func EmptyCmd(db *DB) script.Cmd {
+	return script.Command(
+		script.CmdUsage{
+			Summary: "Assert that given table(s) are empty",
+			Args:    "table",
+		},
+		func(s *script.State, args ...string) (script.WaitFunc, error) {
+			txn := db.ReadTxn()
+			for _, tableName := range args {
+				meta := db.GetTable(txn, tableName)
+				if meta == nil {
+					return nil, fmt.Errorf("table %q not found", tableName)
+				}
+				tbl := AnyTable{Meta: meta}
+				if n := tbl.NumObjects(txn); n != 0 {
+					return nil, fmt.Errorf("table %q not empty, found %d obects", tableName, n)
+				}
+			}
+			return nil, nil
+		})
+}
+
 func InsertCmd(db *DB) script.Cmd {
 	return script.Command(
 		script.CmdUsage{

testdata/db.txtar

@@ -17,11 +17,17 @@ db/initialized test1 test2
 db/show test1
 db/show test2
 
+# Assert empty
+db/empty test1 test2
+
 # Insert
 db/insert test1 obj1.yaml
 db/insert test1 obj2.yaml
 db/insert test2 obj2.yaml
 
+# Assert not empty
+! db/empty test1 test2
+
 # Show (non-empty)
 db/show test1
 stdout ^ID.*Tags