lme(value ~ time * testtype, random = ~ 1 | subject, data = df, na.action = na.omit)

fm <- lme(value ~ 0 + testtype + testtype:type, data = df, na.action = na.omit,
          random = ~ 0 + testtype + testtype:type | subject,
          weights = varIdent(form = ~ 1 | testtype))

summary(fm)

V <- getVarCov(fm, type = "marginal", individual = 1)
R <- cov2cor(V[[1]])
R