diff --git a/tests/testthat/test-challenge.R b/tests/testthat/test-challenge.R
index 69d9061..ea3a179 100644
--- a/tests/testthat/test-challenge.R
+++ b/tests/testthat/test-challenge.R
@@ -1,577 +1,578 @@
 test_that("empty attribute 'taskName' raises error for single-task challenge", {
   data <- rbind(
       data.frame(algo="A1", value=0.8, case="C1"),
       data.frame(algo="A2", value=0.6, case="C1"))
 
   expect_error(as.challenge(data, taskName="", algorithm="algo", case="case", value="value", smallBetter=FALSE),
                "Argument 'taskName' is empty.", fixed=TRUE)
 })
 
 test_that("only whitespaces in attribute 'taskName' raises error for single-task challenge", {
   data <- rbind(
     data.frame(algo="A1", value=0.8, case="C1"),
     data.frame(algo="A2", value=0.6, case="C1"))
 
   expect_error(as.challenge(data, taskName="  ", algorithm="algo", case="case", value="value", smallBetter=FALSE),
                "Argument 'taskName' is empty.", fixed=TRUE)
 })
 
 test_that("attributes are set for single-task challenge with specified task name", {
   data <- rbind(
     data.frame(algo="A1", value=0.8, case="C1"),
     data.frame(algo="A2", value=0.6, case="C1"))
 
   actualChallenge <- as.challenge(data, taskName="T1", algorithm="algo", case="case", value="value", smallBetter=FALSE)
 
   expect_equal(attr(actualChallenge, "annotator"), NULL)
   expect_equal(attr(actualChallenge, "by"), "task")
   expect_equal(attr(actualChallenge, "largeBetter"), TRUE)
   expect_equal(attr(actualChallenge, "check"), TRUE)
 
   expect_equal(as.vector(actualChallenge$T1$algo), c("A1", "A2"))
   expect_equal(as.vector(actualChallenge$T1$value), c(0.8, 0.6))
   expect_equal(as.vector(actualChallenge$T1$case), c("C1", "C1"))
   expect_equal(as.vector(actualChallenge$T1$task), c("T1", "T1"))
 
   # 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 single-task challenge with dummy task name", {
   data <- rbind(
     data.frame(algo="A1", value=0.8, case="C1"),
     data.frame(algo="A2", value=0.6, case="C1"))
 
   actualChallenge <- as.challenge(data, algorithm="algo", case="case", value="value", smallBetter=FALSE)
 
   expect_equal(attr(actualChallenge, "annotator"), NULL)
   expect_equal(attr(actualChallenge, "by"), "task")
   expect_equal(attr(actualChallenge, "largeBetter"), TRUE)
   expect_equal(attr(actualChallenge, "check"), TRUE)
 
   expect_equal(as.vector(actualChallenge$dummyTask$algo), c("A1", "A2"))
   expect_equal(as.vector(actualChallenge$dummyTask$value), c(0.8, 0.6))
   expect_equal(as.vector(actualChallenge$dummyTask$case), c("C1", "C1"))
   expect_equal(as.vector(actualChallenge$dummyTask$task), c("dummyTask", "dummyTask"))
 
   # expect that there's no attribute "task"
   expect_equal(attr(actualChallenge, "task"), NULL)
   expect_equal(attr(actualChallenge$dummyTask, "task"), NULL)
   expect_equal(attr(actualChallenge$dummyTask, "task"), NULL)
 })
 
 test_that("leading and trailing whitespaces are trimmed for attribute 'taskName'", {
   data <- rbind(
     data.frame(algo="A1", value=0.8, case="C1"),
     data.frame(algo="A2", value=0.6, case="C1"))
 
   actualChallenge <- as.challenge(data, taskName=" T1  ", algorithm="algo", case="case", value="value", smallBetter=FALSE)
 
   expect_equal(as.vector(actualChallenge$T1$algo), c("A1", "A2"))
 })
 
 test_that("attributes are set for multi-task challenge", {
   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)
 
   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), c("A1", "A2"))
   expect_equal(as.vector(actualChallenge$T1$value), c(0.8, 0.6))
   expect_equal(as.vector(actualChallenge$T1$case), c("C1", "C1"))
   expect_equal(as.vector(actualChallenge$T1$task), c("T1", "T1"))
 
   expect_equal(as.vector(actualChallenge$T2$algo), c("A1", "A2"))
   expect_equal(as.vector(actualChallenge$T2$value), c(0.2, 0.3))
   expect_equal(as.vector(actualChallenge$T2$case), c("C1", "C1"))
   expect_equal(as.vector(actualChallenge$T2$task), c("T2", "T2"))
 
   # 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)
 
   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$algo), c("A1", "A2", "A1", "A2"))
   expect_equal(as.vector(actualChallenge$value), c(0.8, 0.6, 0.2, 0.3))
   expect_equal(as.vector(actualChallenge$case), c("C1", "C1", "C1", "C1"))
   expect_equal(as.vector(actualChallenge$task), c("T1", "T1", "T2", "T2"))
 })
 
 test_that("attribute 'taskName' is ignored for multi-task challenge", {
   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)
 
   expect_warning(as.challenge(data, taskName="T1", by="task", algorithm="algo", case="case", value="value", smallBetter=TRUE),
                  "Argument 'taskName' is ignored for multi-task data set.", fixed=TRUE)
 })
 
 test_that("missing algorithm performances are added as NAs 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, taskName="T1", 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)
+                 "Performance of not all algorithms has been observed for all cases. Therefore, missings have been inserted in the following cases:", fixed=TRUE)
 
   expect_equal(as.vector(actualChallenge$T1$algo), c("A1", "A1", "A2", "A2"))
   expect_equal(as.vector(actualChallenge$T1$value), c(0.8, NA, NA, 0.6))
   expect_equal(as.vector(actualChallenge$T1$case), c("C1", "C2", "C1", "C2"))
   expect_equal(as.vector(actualChallenge$T1$task), c("T1", "T1", "T1", "T1"))
 })
 
 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, taskName="T1", 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)
+                 "Performance of not all algorithms has been observed for all cases. Therefore, missings have been inserted in the following cases:", fixed=TRUE)
 
   expect_equal(as.vector(actualChallenge$T1$algo), c("A1", "A1", "A2", "A2"))
   expect_equal(as.vector(actualChallenge$T1$value), c(0.8, NA, NA, 0.6))
   expect_equal(as.vector(actualChallenge$T1$case), c("C1", "C2", "C1", "C2"))
 })
 
 test_that("missing algorithm performances are added as NAs 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:", fixed=TRUE)
+                 "Performance of not all algorithms has been observed for all cases in task 'T1'. Therefore, missings have been inserted in the following cases:", fixed=TRUE)
 
   expect_equal(as.vector(actualChallenge$T1$algo), c("A1", "A1", "A2", "A2"))
   expect_equal(as.vector(actualChallenge$T1$value), c(0.8, NA, NA, 0.6))
   expect_equal(as.vector(actualChallenge$T1$case), c("C1", "C2", "C1", "C2"))
   expect_equal(as.vector(actualChallenge$T1$task), c("T1", "T1", "T1", "T1"))
 
   expect_equal(as.vector(actualChallenge$T2$algo), c("A1", "A1", "A2", "A2"))
   expect_equal(as.vector(actualChallenge$T2$value), c(0.2, 0.3, 0.4, NA))
   expect_equal(as.vector(actualChallenge$T2$case), c("C1", "C2", "C1", "C2"))
   expect_equal(as.vector(actualChallenge$T2$task), c("T2", "T2", "T2", "T2"))
 })
 
 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, taskName="T1", algorithm="algo", case="case", value="value", smallBetter=FALSE, check=FALSE)
 
   expect_equal(as.vector(actualChallenge$algo), c("A1", "A2"))
   expect_equal(as.vector(actualChallenge$value), c(0.8, 0.6))
   expect_equal(as.vector(actualChallenge$case), c("C1", "C2"))
 })
 
 test_that("missing algorithm performances are not added as NA with sanity check disabled 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)
 
   actualChallenge <- as.challenge(data, by="task", algorithm="algo", case="case", value="value", smallBetter=FALSE, check=FALSE)
 
   expect_equal(as.vector(actualChallenge$algo), c("A1", "A2", "A1", "A1", "A2"))
   expect_equal(as.vector(actualChallenge$value), c(0.8, 0.6, 0.2, 0.3, 0.4))
   expect_equal(as.vector(actualChallenge$case), c("C1", "C2", "C1", "C2", "C1"))
 })
 
 test_that("case cannot appear more than once per algorithm 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, taskName="T1", algorithm="algo", case="case", value="value", smallBetter=FALSE),
                "The following case(s) appear(s) more than once for the same algorithm. Please revise. Or are you considering a multi-task challenge and forgot to specify argument 'by'?\nCase(s): C1", fixed=TRUE)
 })
 
 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, taskName="T1", algorithm="algo", case="case", value="value", smallBetter=FALSE),
                "The following case(s) appear(s) more than once for the same algorithm. Please revise. Or are you considering a multi-task challenge and forgot to specify argument 'by'?\nCase(s): C1", fixed=TRUE)
 })
 
 test_that("case cannot appear more than once per algorithm 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),
                "The following case(s) appear(s) more than once for the same algorithm. Please revise. Or are you considering a multi-task challenge and forgot to specify argument 'by'?\nCase(s): C1", fixed=TRUE)
 })
 
 test_that("cases cannot appear more than once per algorithm 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, taskName="T1", algorithm="algo", case="case", value="value", smallBetter=FALSE),
                "The following case(s) appear(s) more than once for the same algorithm. Please revise. Or are you considering a multi-task challenge and forgot to specify argument 'by'?\nCase(s): C1, C2", fixed=TRUE)
 })
 
 test_that("cases cannot appear more than once per algorithm 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),
                "The following case(s) appear(s) more than once for the same algorithm. Please revise. Or are you considering a multi-task challenge and forgot to specify argument 'by'?\nCase(s): C1, C2", fixed=TRUE)
 })
 
 test_that("cases cannot appear more than once per algorithm 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),
                "The following case(s) appear(s) more than once for the same algorithm in task 'T2'. Please revise.\nCase(s): C1, C2", fixed=TRUE)
 })
 
 test_that("cases cannot appear more than once per algorithm when missing data was added 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, taskName="T1", algorithm="algo", case="case", value="value", smallBetter=FALSE),
                "The following case(s) appear(s) more than once for the same algorithm. Please revise. Or are you considering a multi-task challenge and forgot to specify argument 'by'?\nCase(s): C1, C2", 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, taskName="New task", algorithm="algo", case="case", value="value", smallBetter=FALSE),
                "The following case(s) appear(s) more than once for the same algorithm. Please revise. Or are you considering a multi-task challenge and forgot to specify argument 'by'?\nCase(s): C1", 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, taskName="New task", 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)
+                 "Performance of not all algorithms has been observed for all cases. Therefore, missings have been inserted in the following cases:", fixed=TRUE)
 })
 
 test_that("NAs are 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, taskName="T1", algorithm="algo", case="case", value="value", smallBetter=FALSE, na.treat=0)
 
   expect_equal(as.vector(actualChallenge$T1$algo), c("A1", "A1", "A2", "A2"))
   expect_equal(as.vector(actualChallenge$T1$value), c(0.8, 0.0, 0.6, 0.0))
   expect_equal(as.vector(actualChallenge$T1$case), c("C1", "C2", "C1", "C2"))
 })
 
 test_that("NAs are replaced by numeric value for multi-task challenge", {
   dataTask1 <- cbind(task="T1",
                      rbind(
                        data.frame(algo="A1", value=0.8, case="C1"),
                        data.frame(algo="A1", value=NA, case="C2")
                      ))
   dataTask2 <- cbind(task="T2",
                      rbind(
                        data.frame(algo="A2", value=NA, case="C1"),
                        data.frame(algo="A2", value=0.5, case="C2")
                      ))
 
   data <- rbind(dataTask1, dataTask2)
 
   actualChallenge <- as.challenge(data, by="task", algorithm="algo", case="case", value="value", smallBetter=FALSE, na.treat=0)
 
   expect_equal(as.vector(actualChallenge$T1$algo), c("A1", "A1"))
   expect_equal(as.vector(actualChallenge$T1$value), c(0.8, 0.0))
   expect_equal(as.vector(actualChallenge$T1$case), c("C1", "C2"))
 
   expect_equal(as.vector(actualChallenge$T2$algo), c("A2", "A2"))
   expect_equal(as.vector(actualChallenge$T2$value), c(0.0, 0.5))
   expect_equal(as.vector(actualChallenge$T2$case), c("C1", "C2"))
 })
 
 test_that("NAs are 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, taskName="T1", algorithm="algo", case="case", value="value", smallBetter=FALSE, na.treat=replacementFunction)
 
   expect_equal(as.vector(actualChallenge$T1$algo), c("A1", "A1", "A2", "A2"))
   expect_equal(as.vector(actualChallenge$T1$value), c(0.8, 2.0, 0.6, 2.0))
   expect_equal(as.vector(actualChallenge$T1$case), c("C1", "C2", "C1", "C2"))
 })
 
 test_that("NAs are replaced by function value for multi-task challenge", {
   dataTask1 <- cbind(task="T1",
                      rbind(
                        data.frame(algo="A1", value=0.8, case="C1"),
                        data.frame(algo="A1", value=NA, case="C2")
                      ))
   dataTask2 <- cbind(task="T2",
                      rbind(
                        data.frame(algo="A2", value=NA, case="C1"),
                        data.frame(algo="A2", value=0.5, case="C2")
                      ))
 
   data <- rbind(dataTask1, dataTask2)
 
   replacementFunction <- function(x) { 2 }
 
   actualChallenge <- as.challenge(data, by="task", algorithm="algo", case="case", value="value", smallBetter=FALSE, na.treat=replacementFunction)
 
   expect_equal(as.vector(actualChallenge$T1$algo), c("A1", "A1"))
   expect_equal(as.vector(actualChallenge$T1$value), c(0.8, 2.0))
   expect_equal(as.vector(actualChallenge$T1$case), c("C1", "C2"))
 
   expect_equal(as.vector(actualChallenge$T2$algo), c("A2", "A2"))
   expect_equal(as.vector(actualChallenge$T2$value), c(2.0, 0.5))
   expect_equal(as.vector(actualChallenge$T2$case), c("C1", "C2"))
 })
 
 test_that("NAs are 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, taskName="T1", algorithm="algo", case="case", value="value", smallBetter=FALSE, na.treat="na.rm")
 
   expect_equal(as.vector(actualChallenge$T1$algo), c("A1", "A2"))
   expect_equal(as.vector(actualChallenge$T1$value), c(0.8, 0.6))
   expect_equal(as.vector(actualChallenge$T1$case), c("C1", "C1"))
 })
 
 test_that("NAs are removed for multi-task challenge", {
   dataTask1 <- cbind(task="T1",
                      rbind(
                        data.frame(algo="A1", value=0.8, case="C1"),
                        data.frame(algo="A1", value=NA, case="C2")
                      ))
   dataTask2 <- cbind(task="T2",
                      rbind(
                        data.frame(algo="A2", value=NA, case="C1"),
                        data.frame(algo="A2", value=0.5, case="C2")
                      ))
 
   data <- rbind(dataTask1, dataTask2)
 
   actualChallenge <- as.challenge(data, by="task", algorithm="algo", case="case", value="value", smallBetter=FALSE, na.treat="na.rm")
 
   expect_equal(as.vector(actualChallenge$T1$algo), c("A1"))
   expect_equal(as.vector(actualChallenge$T1$value), c(0.8))
   expect_equal(as.vector(actualChallenge$T1$case), c("C1"))
 
   expect_equal(as.vector(actualChallenge$T2$algo), c("A2"))
   expect_equal(as.vector(actualChallenge$T2$value), c(0.5))
   expect_equal(as.vector(actualChallenge$T2$case), c("C2"))
 })
 
 test_that("automatically added NAs are replaced by numeric value 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, taskName="T1", algorithm="algo", case="case", value="value", smallBetter=FALSE, na.treat=0),
-                 "Performance of not all algorithms is observed for all cases. Inserted as missings in following cases:", fixed=TRUE)
+                 "Performance of not all algorithms has been observed for all cases. Therefore, missings have been inserted in the following cases:", fixed=TRUE)
 
   expect_equal(as.vector(actualChallenge$T1$algo), c("A1", "A1", "A2", "A2"))
   expect_equal(as.vector(actualChallenge$T1$value), c(0.8, 0.0, 0.0, 0.6))
   expect_equal(as.vector(actualChallenge$T1$case), c("C1", "C2", "C1", "C2"))
 })
 
 test_that("automatically added NAs are replaced by numeric value for multi-task challenge", {
   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, na.treat=0),
-                 "Performance of not all algorithms is observed for all cases in task 'T1'. Inserted as missings in following cases:", fixed=TRUE)
+                 "Performance of not all algorithms has been observed for all cases in task 'T1'. Therefore, missings have been inserted in the following cases:", fixed=TRUE)
 
   expect_equal(as.vector(actualChallenge$T1$algo), c("A1", "A1", "A2", "A2"))
   expect_equal(as.vector(actualChallenge$T1$value), c(0.8, 0.0, 0.0, 0.6))
   expect_equal(as.vector(actualChallenge$T1$case), c("C1", "C2", "C1", "C2"))
 
   expect_equal(as.vector(actualChallenge$T2$algo), c("A1", "A1", "A2", "A2"))
   expect_equal(as.vector(actualChallenge$T2$value), c(0.2, 0.3, 0.4, 0.0))
   expect_equal(as.vector(actualChallenge$T2$case), c("C1", "C2", "C1", "C2"))
 })
 
 test_that("automatically added NAs are removed 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, taskName="T1", algorithm="algo", case="case", value="value", smallBetter=FALSE, na.treat="na.rm"),
-                 "Performance of not all algorithms is observed for all cases. Inserted as missings in following cases:", fixed=TRUE)
+                 "Performance of not all algorithms has been observed for all cases. Therefore, missings have been inserted in the following cases:", fixed=TRUE)
 
   expect_equal(as.vector(actualChallenge$T1$algo), c("A1", "A2"))
   expect_equal(as.vector(actualChallenge$T1$value), c(0.8, 0.6))
   expect_equal(as.vector(actualChallenge$T1$case), c("C1", "C2"))
 })
 
 test_that("automatically added NAs are removed for multi-task challenge", {
   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, na.treat="na.rm"),
-                 "Performance of not all algorithms is observed for all cases in task 'T1'. Inserted as missings in following cases:", fixed=TRUE)
-
+                 "Performance of not all algorithms has been observed for all cases in task 'T1'. Therefore, missings have been inserted in the following cases:", fixed=TRUE)
+  
   expect_equal(as.vector(actualChallenge$T1$algo), c("A1", "A2"))
   expect_equal(as.vector(actualChallenge$T1$value), c(0.8, 0.6))
   expect_equal(as.vector(actualChallenge$T1$case), c("C1", "C2"))
 
   expect_equal(as.vector(actualChallenge$T2$algo), c("A1", "A1", "A2"))
   expect_equal(as.vector(actualChallenge$T2$value), c(0.2, 0.3, 0.4))
   expect_equal(as.vector(actualChallenge$T2$case), c("C1", "C2", "C1"))
 })
+