diff --git a/DESCRIPTION b/DESCRIPTION
index 492ae33..cad592e 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -10,7 +10,7 @@ License: GPL-3
 Encoding: UTF-8
 LazyData: true
 Suggests: 
-    testthat,
+    testthat (>= 2.1.0),
     covr,
     rmarkdown
 RoxygenNote: 6.1.1
diff --git a/NAMESPACE b/NAMESPACE
index d75f824..934d9b3 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -1 +1,5 @@
-exportPattern("^[[:alpha:]]+")
+# Generated by roxygen2: do not edit by hand
+
+export(meanimpute)
+export(transform_log)
+export(windsorize)
diff --git a/R/meanimpute.R b/R/meanimpute.R
index cc7cf5e..d09ca51 100644
--- a/R/meanimpute.R
+++ b/R/meanimpute.R
@@ -1,4 +1,9 @@
 #' Meanimputation
+#'
+#' @param x A numeric vector containing the data
+#' @return the input vector with its NA values replaced by the mean
+#' @examples
+#' log(1:5)
 #' @export
 meanimpute <- function(x) {
   x[is.na(x)] <- mean(x, na.rm = TRUE)
diff --git a/R/transform_log.R b/R/transform_log.R
new file mode 100644
index 0000000..db716d8
--- /dev/null
+++ b/R/transform_log.R
@@ -0,0 +1,17 @@
+#' Log transforms data.
+#'
+#' @param x A numeric vector containing the data
+#' @return A numeric vector whose entries are the logarithms of the input.
+#' @examples
+#' log(1:5)
+#' @export
+transform_log<-function(x){
+  if(length(x)==0){
+    stop("x must have positive length")
+  }else if(sum(x<=0)>0){
+    stop("x must not contain non-positive values")
+  }else if(sum(is.na(x))>0){
+    stop("x must not contain any NA")
+  } 
+  log(x)
+} 
\ No newline at end of file
diff --git a/R/windsorize.R b/R/windsorize.R
index b4e15e6..dba1fda 100644
--- a/R/windsorize.R
+++ b/R/windsorize.R
@@ -1,10 +1,20 @@
-#' Windsorize
+#' Windsorizes data.
 #'
-#' Do some windsorization.
+#' @param x A numeric vector containing the data.
+#' @param p A numeric value denoting the a probability
+#' @return A numeric vector containing the windsorized data, i.e. extreme values are replaced by the quantiles derived from \code{p}.
+#' @examples
+#' windsorize(c(92 , 19 , 101 , 58 , 1053 , 91 , 26 , 78 , 10 , 13 , -40 , 101 , 86 , 85 , 15 , 89 , 89 , 28 , -5 , 41))
 #' @export
 windsorize <- function(x, p = .90) {
-  q <- quantile(x, p)
-  x[x >= q] <- q
+  if(length(x)==0){
+    stop("x must be of positive length")
+  }else if(sum(is.na(x))>0){
+    stop("x must not contain any NA")
+  }
+  q <- quantile(x, 0.5 * ( 1 + p * c(-1,1) ) )
+  x[x >= q[2] ] <- q[2]
+  x[x <= q[1] ] <- q[1] 
   x
 }
 
diff --git a/man/meanimpute.Rd b/man/meanimpute.Rd
index 8139e8f..5984f37 100644
--- a/man/meanimpute.Rd
+++ b/man/meanimpute.Rd
@@ -6,6 +6,15 @@
 \usage{
 meanimpute(x)
 }
+\arguments{
+\item{x}{A numeric vector containing the data}
+}
+\value{
+the input vector with its NA values replaced by the mean
+}
 \description{
 Meanimputation
 }
+\examples{
+log(1:5)
+}
diff --git a/man/transform_log.Rd b/man/transform_log.Rd
new file mode 100644
index 0000000..b7d9dce
--- /dev/null
+++ b/man/transform_log.Rd
@@ -0,0 +1,20 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/transform_log.R
+\name{transform_log}
+\alias{transform_log}
+\title{Log transforms data.}
+\usage{
+transform_log(x)
+}
+\arguments{
+\item{x}{A numeric vector containing the data}
+}
+\value{
+A numeric vector whose entries are the logarithms of the input.
+}
+\description{
+Log transforms data.
+}
+\examples{
+log(1:5)
+}
diff --git a/man/windsorize.Rd b/man/windsorize.Rd
index 832c3cb..ed90eb5 100644
--- a/man/windsorize.Rd
+++ b/man/windsorize.Rd
@@ -2,10 +2,21 @@
 % Please edit documentation in R/windsorize.R
 \name{windsorize}
 \alias{windsorize}
-\title{Windsorize}
+\title{Windsorizes data.}
 \usage{
 windsorize(x, p = 0.9)
 }
+\arguments{
+\item{x}{A numeric vector containing the data.}
+
+\item{p}{A numeric value denoting the a probability}
+}
+\value{
+A numeric vector containing the windsorized data, i.e. extreme values are replaced by the quantiles derived from \code{p}.
+}
 \description{
-Do some windsorization.
+Windsorizes data.
+}
+\examples{
+windsorize(c(92 , 19 , 101 , 58 , 1053 , 91 , 26 , 78 , 10 , 13 , -40 , 101 , 86 , 85 , 15 , 89 , 89 , 28 , -5 , 41))
 }
diff --git a/tests/testthat.R b/tests/testthat.R
new file mode 100644
index 0000000..8adbfff
--- /dev/null
+++ b/tests/testthat.R
@@ -0,0 +1,4 @@
+library(testthat)
+library(datacleaner)
+
+test_check("datacleaner")
diff --git a/tests/testthat/test-windsorize.R b/tests/testthat/test-windsorize.R
new file mode 100644
index 0000000..42d45df
--- /dev/null
+++ b/tests/testthat/test-windsorize.R
@@ -0,0 +1,3 @@
+test_that("windsorize works", {
+  expect_equal(windsorize(3:10), c(3.35,4.00,5.00,6.00,7.00,8.00,9.00,9.65))
+})