         let pageSize = 256
         guard let database = FilePageDatabase(self.tempFilename, size: pageSize) else { XCTFail(); return }
         let treeName = "testvalues"
-        try database.update(version: 101) { (m) in
+        try database.update(version: 101) { (dbm) in
             let pairs: [(UInt32, String)] = []
-            _ = try m.create(tree: treeName, pairs: pairs)
-            guard let t: Tree<UInt32, String> = m.tree(name: treeName) else { fatalError("No such tree") }
+            _ = try dbm.create(tree: treeName, pairs: pairs)
+            guard let t: Tree<UInt32, String> = dbm.tree(name: treeName) else { fatalError("No such tree") }
             for k: UInt32 in 0..<16 {
                 let key = k * 2
                 let value = "<<\(key)>>"


        XCTAssertEqual(database.pageCount, 4)

        try database.read { (m) in
            guard let t: Tree<UInt32, String> = m.tree(name: treeName) else { fatalError("No such tree") }
            do {
                let mtime = try t.effectiveVersion(between: (0, 15))
                XCTAssertNotNil(mtime)

        XCTAssertEqual(database.pageCount, 1)

        let treeName = "testvalues"
        try database.update(version: 101) { (dbm) in
            let pairs: [(UInt32, String)] = []
            _ = try dbm.create(tree: treeName, pairs: pairs)
        }

        XCTAssertEqual(database.pageCount, 2)
        try database.read { (dbm) in
            guard let pid = try? dbm.getRoot(named: treeName) else { XCTFail(); return }
            XCTAssertEqual(pid, 1, "An empty tree created in a fresh database should appear on page 1")
            assertValidTreeVersionMtime(dbm, pid, "tree read 1")
            guard let t: Tree<UInt32, String> = dbm.tree(name: treeName) else { fatalError("No such tree") }
            XCTAssertEqual(t.version, 101)
        }

        try database.update(version: 102) { (dbm) in
            guard let t: Tree<UInt32, String> = dbm.tree(name: treeName) else { fatalError("No such tree") }
            for k: UInt32 in 0..<14 {
                let key = k * 2
                let value = "<<\(key)>>"
