diff --git a/tests/testthat/test-challenge.R b/tests/testthat/test-challenge.R
index 389a0ef..b608ea5 100644
--- a/tests/testthat/test-challenge.R
+++ b/tests/testthat/test-challenge.R
@@ -1,106 +1,142 @@
 test_that("missing algorithm performances are added as NA with sanity check enabled for single-task challenge", {
   data=rbind(
          data.frame(alg_name="A1", value=0.8, case="C1"),
          data.frame(alg_name="A2", value=0.6, case="C2")
        )
 
   expect_message(actualChallenge <- as.challenge(data, algorithm="alg_name", case="case", value="value", smallBetter=FALSE),
                  "Performance of not all algorithms is observed for all cases. Inserted as missings in following cases:")
 
   expectedAlgNames <- c("A1", "A1", "A2", "A2")
   expectedValues <- c(0.8, NA, NA, 0.6)
   expectedCases <- c("C1", "C2", "C1", "C2")
 
   expect_equal(as.vector(actualChallenge$alg_name), expectedAlgNames)
   expect_equal(as.vector(actualChallenge$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(alg_name="A1", value=0.8, case="C1"),
          data.frame(alg_name="A2", value=0.6, case="C2")
        )
 
   actualChallenge <- as.challenge(data, algorithm="alg_name", case="case", value="value", smallBetter=FALSE, check=FALSE)
 
-   expectedAlgNames <- c("A1", "A2")
+  expectedAlgNames <- c("A1", "A2")
   expectedValues <- c(0.8, 0.6)
   expectedCases <- c("C1", "C2")
 
   expect_equal(as.vector(actualChallenge$alg_name), expectedAlgNames)
   expect_equal(as.vector(actualChallenge$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(alg_name="A1", value=0.8, case="C1"),
                data.frame(alg_name="A2", value=0.6, case="C2")
              ))
 
   expect_message(actualChallenge <- as.challenge(data, by="task", algorithm="alg_name", 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:")
 
   expectedAlgNames <- c("A1", "A1", "A2", "A2")
   expectedValues <- c(0.8, NA, NA, 0.6)
   expectedCases <- c("C1", "C2", "C1", "C2")
 
   expect_equal(as.vector(actualChallenge$T1$alg_name), expectedAlgNames)
   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(alg_name="A1", value=0.8, case="C1"),
                data.frame(alg_name="A2", value=0.6, case="C2")
              ))
 
   actualChallenge <- as.challenge(data, by="task", algorithm="alg_name", case="case", value="value", smallBetter=FALSE, check=FALSE)
 
   expectedAlgNames <- c("A1", "A2")
   expectedValues <- c(0.8, 0.6)
   expectedCases <- c("C1", "C2")
 
   expect_equal(as.vector(actualChallenge$alg_name), expectedAlgNames)
   expect_equal(as.vector(actualChallenge$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)", {
   dataT1=cbind(task="T1",
                rbind(
                  data.frame(alg_name="A1", value=0.8, case="C1"),
                  data.frame(alg_name="A2", value=0.6, case="C2")
                ))
   dataT2=cbind(task="T2",
                rbind(
                  data.frame(alg_name="A1", value=0.2, case="C1"),
                  data.frame(alg_name="A1", value=0.3, case="C2"),
                  data.frame(alg_name="A2", value=0.4, case="C1")
                ))
 
   data=rbind(dataT1, dataT2)
 
   expect_message(actualChallenge <- as.challenge(data, by="task", algorithm="alg_name", 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:")
 
   expectedAlgNamesT1 <- c("A1", "A1", "A2", "A2")
   expectedValuesT1 <- c(0.8, NA, NA, 0.6)
   expectedCasesT1 <- c("C1", "C2", "C1", "C2")
 
   expect_equal(as.vector(actualChallenge$T1$alg_name), expectedAlgNamesT1)
   expect_equal(as.vector(actualChallenge$T1$value), expectedValuesT1)
   expect_equal(as.vector(actualChallenge$T1$case), expectedCasesT1)
 
   expectedAlgNamesT2 <- 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$T2$alg_name), expectedAlgNamesT2)
   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(alg_name="A1", value=0.8, case="C1"),
+    data.frame(alg_name="A1", value=0.8, case="C1")
+  )
+
+  expect_error(as.challenge(data, algorithm="alg_name", 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(alg_name="A1", value=0.8, case="C1"),
+    data.frame(alg_name="A1", value=0.8, case="C1"),
+    data.frame(alg_name="A2", value=0.7, case="C1"),
+    data.frame(alg_name="A1", value=0.5, case="C2"),
+    data.frame(alg_name="A2", value=0.6, case="C2"),
+    data.frame(alg_name="A2", value=0.6, case="C2")
+  )
+
+  expect_error(as.challenge(data, algorithm="alg_name", 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(alg_name="A1", value=0.8, case="C1"),
+    data.frame(alg_name="A1", value=0.8, case="C1"),
+    data.frame(alg_name="A2", value=0.6, case="C2"),
+    data.frame(alg_name="A2", value=0.6, case="C2")
+  )
+
+  expect_error(as.challenge(data, algorithm="alg_name", case="case", value="value", smallBetter=FALSE),
+               "Case(s) (C1, C2) appear(s) more than once for the same algorithm", fixed=TRUE)
+})