diff --git a/tests/testthat/test-challenge.R b/tests/testthat/test-challenge.R
index 827eec7..ac7613e 100644
--- a/tests/testthat/test-challenge.R
+++ b/tests/testthat/test-challenge.R
@@ -1,359 +1,418 @@
 test_that("attributes are set for single-task challenge", {
   data=rbind(
     data.frame(algo="A1", value=0.8, case="C1"),
     data.frame(algo="A1", value=0.4, case="C2"),
     data.frame(algo="A2", value=0.6, case="C1"),
     data.frame(algo="A2", value=0.7, case="C2")
   )
 
   actualChallenge <- as.challenge(data, algorithm="algo", case="case", value="value", smallBetter=FALSE)
 
   expectedAlgorithms <- c("A1", "A1", "A2", "A2")
   expectedValues <- c(0.8, 0.4, 0.6, 0.7)
   expectedCases <- c("C1", "C2", "C1", "C2")
 
   expect_equal(attr(actualChallenge, "annotator"), NULL)
   expect_equal(attr(actualChallenge, "by"), NULL)
   expect_equal(attr(actualChallenge, "largeBetter"), TRUE)
   expect_equal(attr(actualChallenge, "check"), TRUE)
   expect_equal(as.vector(actualChallenge$algo), expectedAlgorithms)
   expect_equal(as.vector(actualChallenge$value), expectedValues)
   expect_equal(as.vector(actualChallenge$case), expectedCases)
 })
 
 test_that("attributes are set for multi-task challenge with sanity check enabled", {
   dataTask1=cbind(task="T1",
                   rbind(
                     data.frame(algo="A1", value=0.8, case="C1"),
                     data.frame(algo="A2", value=0.6, case="C1")
                   ))
   dataTask2=cbind(task="T2",
                   rbind(
                     data.frame(algo="A1", value=0.2, case="C1"),
                     data.frame(algo="A2", value=0.3, case="C1")
                   ))
 
   data=rbind(dataTask1, dataTask2)
 
   actualChallenge <- as.challenge(data, by="task", algorithm="algo", case="case", value="value", smallBetter=TRUE, check=TRUE)
 
   expectedAlgorithmsTask1 <- c("A1", "A2")
   expectedValuesTask1 <- c(0.8, 0.6)
   expectedCasesTask1 <- c("C1", "C1")
   expectedTasksTask1 <- c("T1", "T1")
 
   expectedAlgorithmsTask2 <- c("A1", "A2")
   expectedValuesTask2 <- c(0.2, 0.3)
   expectedCasesTask2 <- c("C1", "C1")
   expectedTasksTask2 <- c("T2", "T2")
 
   expect_equal(attr(actualChallenge, "annotator"), NULL)
   expect_equal(attr(actualChallenge, "by"), "task")
   expect_equal(attr(actualChallenge, "largeBetter"), FALSE)
   expect_equal(attr(actualChallenge, "check"), TRUE)
 
   expect_equal(as.vector(actualChallenge$T1$algo), expectedAlgorithmsTask1)
   expect_equal(as.vector(actualChallenge$T1$value), expectedValuesTask1)
   expect_equal(as.vector(actualChallenge$T1$case), expectedCasesTask1)
   expect_equal(as.vector(actualChallenge$T1$task), expectedTasksTask1)
 
   expect_equal(as.vector(actualChallenge$T2$algo), expectedAlgorithmsTask2)
   expect_equal(as.vector(actualChallenge$T2$value), expectedValuesTask2)
   expect_equal(as.vector(actualChallenge$T2$case), expectedCasesTask2)
   expect_equal(as.vector(actualChallenge$T2$task), expectedTasksTask2)
 
   # expect that there's no attribute "task"
   expect_equal(attr(actualChallenge, "task"), NULL)
   expect_equal(attr(actualChallenge$T1, "task"), NULL)
   expect_equal(attr(actualChallenge$T2, "task"), NULL)
 })
 
 test_that("attributes are set for multi-task challenge with sanity check disabled", {
   dataTask1=cbind(task="T1",
                   rbind(
                     data.frame(algo="A1", value=0.8, case="C1"),
                     data.frame(algo="A2", value=0.6, case="C1")
                   ))
   dataTask2=cbind(task="T2",
                   rbind(
                     data.frame(algo="A1", value=0.2, case="C1"),
                     data.frame(algo="A2", value=0.3, case="C1")
                   ))
 
   data=rbind(dataTask1, dataTask2)
 
   actualChallenge <- as.challenge(data, by="task", algorithm="algo", case="case", value="value", smallBetter=TRUE, check=FALSE)
 
   expectedAlgorithms <- c("A1", "A2", "A1", "A2")
   expectedValues <- c(0.8, 0.6, 0.2, 0.3)
   expectedCases <- c("C1", "C1", "C1", "C1")
   expectedTasks <- c("T1", "T1", "T2", "T2")
 
   expect_equal(attr(actualChallenge, "annotator"), NULL)
   expect_equal(attr(actualChallenge, "by"), "task")
   expect_equal(attr(actualChallenge, "largeBetter"), FALSE)
   expect_equal(attr(actualChallenge, "check"), FALSE)
   expect_equal(as.vector(actualChallenge$algo), expectedAlgorithms)
   expect_equal(as.vector(actualChallenge$value), expectedValues)
   expect_equal(as.vector(actualChallenge$case), expectedCases)
   expect_equal(as.vector(actualChallenge$task), expectedTasks)
 })
 
 test_that("missing algorithm performances are added as NA with sanity check enabled for single-task challenge", {
   data=rbind(
          data.frame(algo="A1", value=0.8, case="C1"),
          data.frame(algo="A2", value=0.6, case="C2")
        )
 
   expect_message(actualChallenge <- as.challenge(data, algorithm="algo", case="case", value="value", smallBetter=FALSE),
                  "Performance of not all algorithms is observed for all cases. Inserted as missings in following cases:")
 
   expectedAlgorithms <- c("A1", "A1", "A2", "A2")
   expectedValues <- c(0.8, NA, NA, 0.6)
   expectedCases <- c("C1", "C2", "C1", "C2")
 
   expect_equal(as.vector(actualChallenge$algo), expectedAlgorithms)
   expect_equal(as.vector(actualChallenge$value), expectedValues)
   expect_equal(as.vector(actualChallenge$case), expectedCases)
 })
 
 test_that("missing algorithm performances are not added as NA with sanity check disabled for single-task challenge", {
   data=rbind(
          data.frame(algo="A1", value=0.8, case="C1"),
          data.frame(algo="A2", value=0.6, case="C2")
        )
 
   actualChallenge <- as.challenge(data, algorithm="algo", case="case", value="value", smallBetter=FALSE, check=FALSE)
 
   expectedAlgorithms <- c("A1", "A2")
   expectedValues <- c(0.8, 0.6)
   expectedCases <- c("C1", "C2")
 
   expect_equal(as.vector(actualChallenge$algo), expectedAlgorithms)
   expect_equal(as.vector(actualChallenge$value), expectedValues)
   expect_equal(as.vector(actualChallenge$case), expectedCases)
 })
 
 test_that("missing algorithm performances are added as NA with sanity check enabled for multi-task challenge (1 task in data set)", {
   data=cbind(task="T1",
              rbind(
                data.frame(algo="A1", value=0.8, case="C1"),
                data.frame(algo="A2", value=0.6, case="C2")
              ))
 
   expect_message(actualChallenge <- as.challenge(data, by="task", algorithm="algo", case="case", value="value", smallBetter=FALSE),
                  "Performance of not all algorithms is observed for all cases in task T1. Inserted as missings in following cases:")
 
   expectedAlgorithms <- c("A1", "A1", "A2", "A2")
   expectedValues <- c(0.8, NA, NA, 0.6)
   expectedCases <- c("C1", "C2", "C1", "C2")
 
   expect_equal(as.vector(actualChallenge$T1$algo), expectedAlgorithms)
   expect_equal(as.vector(actualChallenge$T1$value), expectedValues)
   expect_equal(as.vector(actualChallenge$T1$case), expectedCases)
 })
 
 test_that("missing algorithm performances are not added as NA with sanity check disabled for multi-task challenge (1 task in data set)", {
   data=cbind(task="T1",
              rbind(
                data.frame(algo="A1", value=0.8, case="C1"),
                data.frame(algo="A2", value=0.6, case="C2")
              ))
 
   actualChallenge <- as.challenge(data, by="task", algorithm="algo", case="case", value="value", smallBetter=FALSE, check=FALSE)
 
   expectedAlgorithms <- c("A1", "A2")
   expectedValues <- c(0.8, 0.6)
   expectedCases <- c("C1", "C2")
 
   expect_equal(as.vector(actualChallenge$algo), expectedAlgorithms)
   expect_equal(as.vector(actualChallenge$value), expectedValues)
   expect_equal(as.vector(actualChallenge$case), expectedCases)
 })
 
 test_that("missing algorithm performances are added as NA with sanity check enabled for multi-task challenge (2 tasks in data set)", {
   dataTask1=cbind(task="T1",
                rbind(
                  data.frame(algo="A1", value=0.8, case="C1"),
                  data.frame(algo="A2", value=0.6, case="C2")
                ))
   dataTask2=cbind(task="T2",
                rbind(
                  data.frame(algo="A1", value=0.2, case="C1"),
                  data.frame(algo="A1", value=0.3, case="C2"),
                  data.frame(algo="A2", value=0.4, case="C1")
                ))
 
   data=rbind(dataTask1, dataTask2)
 
   expect_message(actualChallenge <- as.challenge(data, by="task", algorithm="algo", case="case", value="value", smallBetter=FALSE),
                  "Performance of not all algorithms is observed for all cases in task T1. Inserted as missings in following cases:")
 
   expectedAlgorithmsTask1 <- c("A1", "A1", "A2", "A2")
   expectedValuesT1 <- c(0.8, NA, NA, 0.6)
   expectedCasesT1 <- c("C1", "C2", "C1", "C2")
 
   expect_equal(as.vector(actualChallenge$T1$algo), expectedAlgorithmsTask1)
   expect_equal(as.vector(actualChallenge$T1$value), expectedValuesT1)
   expect_equal(as.vector(actualChallenge$T1$case), expectedCasesT1)
 
   expectedAlgorithmsTask2 <- c("A1", "A1", "A2", "A2")
   expectedValuesT2 <- c(0.2, 0.3, 0.4, NA)
   expectedCasesT2 <- c("C1", "C2", "C1", "C2")
 
   expect_equal(as.vector(actualChallenge$T2$algo), expectedAlgorithmsTask2)
   expect_equal(as.vector(actualChallenge$T2$value), expectedValuesT2)
   expect_equal(as.vector(actualChallenge$T2$case), expectedCasesT2)
 })
 
 test_that("case cannot appear more than once per algorithm with sanity check enabled for single-task challenge", {
   data=rbind(
     data.frame(algo="A1", value=0.8, case="C1"),
     data.frame(algo="A1", value=0.8, case="C1")
   )
 
   expect_error(as.challenge(data, algorithm="algo", case="case", value="value", smallBetter=FALSE),
                "Case(s) (C1) appear(s) more than once for the same algorithm", fixed=TRUE)
 })
 
 test_that("cases cannot appear more than once per algorithm with sanity check enabled for single-task challenge", {
   data=rbind(
     data.frame(algo="A1", value=0.8, case="C1"),
     data.frame(algo="A1", value=0.8, case="C1"),
     data.frame(algo="A2", value=0.7, case="C1"),
     data.frame(algo="A1", value=0.5, case="C2"),
     data.frame(algo="A2", value=0.6, case="C2"),
     data.frame(algo="A2", value=0.6, case="C2")
   )
 
   expect_error(as.challenge(data, algorithm="algo", case="case", value="value", smallBetter=FALSE),
                "Case(s) (C1, C2) appear(s) more than once for the same algorithm", fixed=TRUE)
 })
 
 test_that("cases cannot appear more than once per algorithm when missing data was added with sanity check enabled for single-task challenge", {
   data=rbind(
     data.frame(algo="A1", value=0.8, case="C1"),
     data.frame(algo="A1", value=0.8, case="C1"),
     data.frame(algo="A2", value=0.6, case="C2"),
     data.frame(algo="A2", value=0.6, case="C2")
   )
 
   expect_error(as.challenge(data, algorithm="algo", case="case", value="value", smallBetter=FALSE),
                "Case(s) (C1, C2) appear(s) more than once for the same algorithm", fixed=TRUE)
 })
 
 test_that("case cannot appear more than once per algorithm with sanity check enabled for multi-task challenge (1 task in data set)", {
   data=cbind(task="T1",
              rbind(
                data.frame(algo="A1", value=0.8, case="C1"),
                data.frame(algo="A1", value=0.8, case="C1")
              ))
 
   expect_error(as.challenge(data, by="task", algorithm="algo", case="case", value="value", smallBetter=FALSE),
                "Case(s) (C1) appear(s) more than once for the same algorithm in task T1", fixed=TRUE)
 })
 
 test_that("cases cannot appear more than once per algorithm with sanity check enabled for multi-task challenge (1 task in data set)", {
   data=cbind(task="T1",
              rbind(
                data.frame(algo="A1", value=0.8, case="C1"),
                data.frame(algo="A1", value=0.8, case="C1"),
                data.frame(algo="A2", value=0.7, case="C1"),
                data.frame(algo="A1", value=0.5, case="C2"),
                data.frame(algo="A2", value=0.6, case="C2"),
                data.frame(algo="A2", value=0.6, case="C2")
              ))
 
   expect_error(as.challenge(data, by="task", algorithm="algo", case="case", value="value", smallBetter=FALSE),
                "Case(s) (C1, C2) appear(s) more than once for the same algorithm in task T1", fixed=TRUE)
 })
 
 test_that("cases cannot appear more than once per algorithm with sanity check enabled for multi-task challenge (2 tasks in data set)", {
   dataTask1=cbind(task="T1",
                   rbind(
                     data.frame(algo="A1", value=0.8, case="C1") # let T1 pass
                   ))
 
   dataTask2=cbind(task="T2",
                   rbind(
                     data.frame(algo="A1", value=0.8, case="C1"),
                     data.frame(algo="A1", value=0.8, case="C1"),
                     data.frame(algo="A2", value=0.7, case="C1"),
                     data.frame(algo="A1", value=0.5, case="C2"),
                     data.frame(algo="A2", value=0.6, case="C2"),
                     data.frame(algo="A2", value=0.6, case="C2")
                   ))
 
   data=rbind(dataTask1, dataTask2)
 
   expect_error(as.challenge(data, by="task", algorithm="algo", case="case", value="value", smallBetter=FALSE),
                "Case(s) (C1, C2) appear(s) more than once for the same algorithm in task T2", fixed=TRUE)
 })
 
 test_that("multi-task data set containing one task is interpreted as single-task data set, missing algorithm performances are added", {
   data=cbind(task="T1",
              rbind(
                data.frame(algo="A1", value=0.8, case="C1"),
                data.frame(algo="A2", value=0.6, case="C2")
              ))
 
   # do not specify parameter "by" to interpret multi-task data set as single-task data set
   expect_message(actualChallenge <- as.challenge(data, algorithm="algo", case="case", value="value", smallBetter=FALSE),
                  "Performance of not all algorithms is observed for all cases. Inserted as missings in following cases:")
 
   expectedAlgorithms <- c("A1", "A1", "A2", "A2")
   expectedValues <- c(0.8, NA, NA, 0.6)
   expectedCases <- c("C1", "C2", "C1", "C2")
 
   expect_equal(as.vector(actualChallenge$algo), expectedAlgorithms)
   expect_equal(as.vector(actualChallenge$value), expectedValues)
   expect_equal(as.vector(actualChallenge$case), expectedCases)
 })
 
 test_that("multi-task data set containing one task is interpreted as single-task data set, case cannot appear more than once per algorithm", {
   data=cbind(task="T1",
              rbind(
                data.frame(algo="A1", value=0.8, case="C1"),
                data.frame(algo="A1", value=0.8, case="C1")
              ))
 
   # do not specify parameter "by" to interpret multi-task data set as single-task data set
   expect_error(as.challenge(data, algorithm="algo", case="case", value="value", smallBetter=FALSE),
                "Case(s) (C1) appear(s) more than once for the same algorithm", fixed=TRUE)
 })
 
 test_that("user is notified of duplicate cases when multi-task data set is interpreted as single-task data set (2 tasks in data set)", {
   dataTask1=cbind(task="T1",
                   rbind(
                     data.frame(algo="A1", value=0.8, case="C1")
                   ))
 
   dataTask2=cbind(task="T2",
                   rbind(
                     data.frame(algo="A1", value=0.8, case="C1")
                   ))
 
   data=rbind(dataTask1, dataTask2)
 
   # do not specify parameter "by" to interpret multi-task data set as single-task data set
   expect_error(as.challenge(data, algorithm="algo", case="case", value="value", smallBetter=FALSE),
                "Case(s) (C1) appear(s) more than once for the same algorithm", fixed=TRUE)
 })
 
 test_that("user is notified of missing algorithm performance when multi-task data set is interpreted as single-task data set (2 tasks in data set)", {
   dataTask1=cbind(task="T1",
                   rbind(
                     data.frame(algo="A1", value=0.8, case="C1")
                   ))
 
   dataTask2=cbind(task="T2",
                   rbind(
                     data.frame(algo="A2", value=0.6, case="C2")
                   ))
 
   data=rbind(dataTask1, dataTask2)
 
   # do not specify parameter "by" to interpret multi-task data set as single-task data set
   expect_message(as.challenge(data, algorithm="algo", case="case", value="value", smallBetter=FALSE),
                "Performance of not all algorithms is observed for all cases. Inserted as missings in following cases:", fixed=TRUE)
 })
+
+test_that("NA is replaced by numeric value for single-task challenge", {
+  data=rbind(
+    data.frame(algo="A1", value=0.8, case="C1"),
+    data.frame(algo="A1", value=NA, case="C2"),
+    data.frame(algo="A2", value=0.6, case="C1"),
+    data.frame(algo="A2", value=NA, case="C2")
+  )
+
+  actualChallenge <- as.challenge(data, algorithm="algo", case="case", value="value", smallBetter=FALSE, na.treat=0)
+
+  expectedAlgorithms <- c("A1", "A1", "A2", "A2")
+  expectedValues <- c(0.8, 0.0, 0.6, 0.0)
+  expectedCases <- c("C1", "C2", "C1", "C2")
+
+  expect_equal(as.vector(actualChallenge$algo), expectedAlgorithms)
+  expect_equal(as.vector(actualChallenge$value), expectedValues)
+  expect_equal(as.vector(actualChallenge$case), expectedCases)
+})
+
+test_that("NA is replaced by function value for single-task challenge", {
+  data=rbind(
+    data.frame(algo="A1", value=0.8, case="C1"),
+    data.frame(algo="A1", value=NA, case="C2"),
+    data.frame(algo="A2", value=0.6, case="C1"),
+    data.frame(algo="A2", value=NA, case="C2")
+  )
+
+  replacementFunction <- function(x) { 2 }
+
+  actualChallenge <- as.challenge(data, algorithm="algo", case="case", value="value", smallBetter=FALSE, na.treat=replacementFunction)
+
+  expectedAlgorithms <- c("A1", "A1", "A2", "A2")
+  expectedValues <- c(0.8, 2.0, 0.6, 2.0)
+  expectedCases <- c("C1", "C2", "C1", "C2")
+
+  expect_equal(as.vector(actualChallenge$algo), expectedAlgorithms)
+  expect_equal(as.vector(actualChallenge$value), expectedValues)
+  expect_equal(as.vector(actualChallenge$case), expectedCases)
+})
+
+test_that("NA is removed for single-task challenge", {
+  data=rbind(
+    data.frame(algo="A1", value=0.8, case="C1"),
+    data.frame(algo="A1", value=NA, case="C2"),
+    data.frame(algo="A2", value=0.6, case="C1"),
+    data.frame(algo="A2", value=NA, case="C2")
+  )
+
+  actualChallenge <- as.challenge(data, algorithm="algo", case="case", value="value", smallBetter=FALSE, na.treat="na.rm")
+
+  expectedAlgorithms <- c("A1", "A2")
+  expectedValues <- c(0.8, 0.6)
+  expectedCases <- c("C1", "C1")
+
+  expect_equal(as.vector(actualChallenge$algo), expectedAlgorithms)
+  expect_equal(as.vector(actualChallenge$value), expectedValues)
+  expect_equal(as.vector(actualChallenge$case), expectedCases)
+})
\ No newline at end of file