diff --git a/DESCRIPTION b/DESCRIPTION
index 492ae33..9aecf04 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -4,6 +4,7 @@ Title: Data Cleaning - what else?
 Version: 0.1.0
 Author: Quantargo Instructor
 Maintainer: Quantargo Instructor <courses@quantargo.com>
+Imports: stats
 Description: Some lengthy description which somebody should write
     Sometime.
 License: GPL-3
diff --git a/NAMESPACE b/NAMESPACE
index d75f824..1015c5a 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -1 +1,2 @@
 exportPattern("^[[:alpha:]]+")
+importFrom("stats", "quantile")
\ No newline at end of file
diff --git a/R/meanimpute.R b/R/meanimpute.R
index cc7cf5e..5a58f8d 100644
--- a/R/meanimpute.R
+++ b/R/meanimpute.R
@@ -1,5 +1,14 @@
 #' Meanimputation
+#'
+#' Replaces NA values with the mean of \code{x}
+#' 
+#' @param x A numeric vector containing real numbers
+#' @return Imputed vector \code{x} where NAs are replaced with the mean of \code{x}
+#' @examples
+#' meanimpute(x = c(1, NA, 3, 4, 5, 6, 7, 8, NA, 10))
+#' meanimpute(c(1, NA, 3, 4, 5, 6, 7, 8, NA, 10))
 #' @export
+
 meanimpute <- function(x) {
   x[is.na(x)] <- mean(x, na.rm = TRUE)
   x
diff --git a/R/transform_log.R b/R/transform_log.R
new file mode 100644
index 0000000..244ed48
--- /dev/null
+++ b/R/transform_log.R
@@ -0,0 +1,26 @@
+#' Transform_log
+#'
+#' Transforms values to natural logarithm.
+#' 
+#' @param x A numeric vector containing positive real numbers
+#' @return Natural logarithm of the values in \code{x}.
+#' @examples
+#' transform_log(x = c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10))
+#' transform_log(c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10))
+#' @export
+
+transform_log <- function(x){
+  
+  if( sum(is.na(x)) ){
+    stop("Input x contains value NA")
+  }
+  else if( length(x) == 0 ){
+    stop("Input x is NULL")
+  }  
+  else if( sum(x <= 0)  ){
+    stop("Input x contains non-positive values")
+  }  
+  
+  log(x)
+  
+}
diff --git a/R/windsorize.R b/R/windsorize.R
index b4e15e6..51e0bd3 100644
--- a/R/windsorize.R
+++ b/R/windsorize.R
@@ -1,10 +1,29 @@
 #' Windsorize
 #'
 #' Do some windsorization.
+#' 
+#' @param x A numeric vector containing real numbers
+#' @param p A number between 0 and 1, representing the mass of probability. Values are winsorized outside \code{p}. Default value is 0.9. 
+#' @return Windsorized vector of \code{x}.
+#' @examples
+#' windsorize(x = c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10))
+#' windsorize(x = c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10), p = 0.8)
+#' windsorize(c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10), 0.8)
 #' @export
+
 windsorize <- function(x, p = .90) {
-  q <- quantile(x, p)
-  x[x >= q] <- q
+  
+  if( sum(is.na(x))){
+    stop("Input x contains value NA")
+  }
+  else if( length(x) == 0 ){
+    stop("Input x is NULL")
+  }
+  
+  q_lower <- quantile(x, (1-p)/2)
+  q_upper <- quantile(x, p + (1-p)/2)
+  x[x <= q_lower] <- q_lower
+  x[x >= q_upper] <- q_upper
   x
 }
 
diff --git a/man/meanimpute.Rd b/man/meanimpute.Rd
index 8139e8f..7c4032c 100644
--- a/man/meanimpute.Rd
+++ b/man/meanimpute.Rd
@@ -6,6 +6,16 @@
 \usage{
 meanimpute(x)
 }
+\arguments{
+\item{x}{A numeric vector containing real numbers}
+}
+\value{
+Imputed vector \code{x} where NAs are replaced with the mean of \code{x}
+}
 \description{
-Meanimputation
+Replaces NA values with the mean of \code{x}
+}
+\examples{
+meanimpute(x = c(1, NA, 3, 4, 5, 6, 7, 8, NA, 10))
+meanimpute(c(1, NA, 3, 4, 5, 6, 7, 8, NA, 10))
 }
diff --git a/man/transform_log.Rd b/man/transform_log.Rd
new file mode 100644
index 0000000..3a172e8
--- /dev/null
+++ b/man/transform_log.Rd
@@ -0,0 +1,21 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/transform_log.R
+\name{transform_log}
+\alias{transform_log}
+\title{Transform_log}
+\usage{
+transform_log(x)
+}
+\arguments{
+\item{x}{A numeric vector containing positive real numbers}
+}
+\value{
+Natural logarithm of the values in \code{x}.
+}
+\description{
+Transforms values to natural logarithm.
+}
+\examples{
+transform_log(x = c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10))
+transform_log(c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10))
+}
diff --git a/man/windsorize.Rd b/man/windsorize.Rd
index 832c3cb..2d73fd4 100644
--- a/man/windsorize.Rd
+++ b/man/windsorize.Rd
@@ -6,6 +6,19 @@
 \usage{
 windsorize(x, p = 0.9)
 }
+\arguments{
+\item{x}{A numeric vector containing real numbers}
+
+\item{p}{A number between 0 and 1, representing the mass of probability. Values are winsorized outside \code{p}. Default value is 0.9.}
+}
+\value{
+Windsorized vector of \code{x}.
+}
 \description{
 Do some windsorization.
 }
+\examples{
+windsorize(x = c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10))
+windsorize(x = c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10), p = 0.8)
+windsorize(c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10), 0.8)
+}
diff --git a/tests/testthat.R b/tests/testthat.R
new file mode 100644
index 0000000..2a036fa
--- /dev/null
+++ b/tests/testthat.R
@@ -0,0 +1,4 @@
+library(testthat)
+library(datacleaner)
+
+test_check("datacleaner")
\ No newline at end of file
diff --git a/tests/testthat/testthat.R b/tests/testthat/testthat.R
new file mode 100644
index 0000000..1f69b30
--- /dev/null
+++ b/tests/testthat/testthat.R
@@ -0,0 +1,19 @@
+library(datacleaner)
+
+test_that("windsorize the input vector", {
+  expect_error(windsorize(c(NULL)), "Input x is NULL")
+  expect_error(windsorize(c(1, 2, NA)), "Input x contains value NA")
+  expect_equal(windsorize(c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10), 0.8), c(1.9, 2, 3, 4, 5, 6, 7, 8, 9, 9.1))
+})
+
+test_that("Takes natural logarithm", {
+  expect_error(transform_log(c(NULL)), "Input x is NULL")
+  expect_error(transform_log(c(1, 2, NA)), "Input x contains value NA")
+  expect_error(transform_log(c(-1, 2, 3)), "Input x contains non-positive values")
+  expect_equal(transform_log(c(1, exp(1))), c(0, 1))
+})
+
+test_that("Takes natural logarithm", {
+  expect_equal(meanimpute(c(1, NA, 3)), c(1, 2, 3))
+  expect_equal(meanimpute(c(1, 2 , 3)), c(1, 2, 3))
+})
\ No newline at end of file