wantStr string
			wantErr error
		}
		testWriteTo struct { // WriteTo(testFile{ops}) == (wantCnt, wantErr)
			ops     fileOps
			wantCnt int64
			wantErr error
		}
		testRemaining struct { // logicalRemaining() == wantLCnt, physicalRemaining() == wantPCnt
			wantLCnt int64
			wantPCnt int64
		}
		testFnc any // testRead | testWriteTo | testRemaining
	)

	type (
		makeReg struct {