diff --git a/fetchall/main_test.go b/fetchall/main_test.go
index 71c3855..2dca656 100644
--- a/fetchall/main_test.go
+++ b/fetchall/main_test.go
@@ -35,7 +35,7 @@ func TestMain(m *testing.M) {
 
 func TestFetchall_valid(t *testing.T) {
 	binary, err := binCache.GetBinary(fetchallImportPath)
-	require.Nil(t, err)
+	require.NoError(t, err)
 
 	type endpoint string
 
@@ -73,14 +73,14 @@ func TestFetchall_valid(t *testing.T) {
 			cmd.Stdout = nil
 			cmd.Stderr = os.Stderr
 
-			require.Nil(t, cmd.Run())
+			require.NoError(t, cmd.Run())
 		})
 	}
 }
 
 func TestFetchall_multipleURLs(t *testing.T) {
 	binary, err := binCache.GetBinary(fetchallImportPath)
-	require.Nil(t, err)
+	require.NoError(t, err)
 
 	var fooHit, barHit int32
 
@@ -101,7 +101,7 @@ func TestFetchall_multipleURLs(t *testing.T) {
 	cmd.Stdout = nil
 	cmd.Stderr = os.Stderr
 
-	require.Nil(t, cmd.Run())
+	require.NoError(t, cmd.Run())
 
 	require.Equal(t, int32(1), atomic.LoadInt32(&fooHit))
 	require.Equal(t, int32(1), atomic.LoadInt32(&barHit))
@@ -109,7 +109,7 @@ func TestFetchall_multipleURLs(t *testing.T) {
 
 func TestFetchall_malformed(t *testing.T) {
 	binary, err := binCache.GetBinary(fetchallImportPath)
-	require.Nil(t, err)
+	require.NoError(t, err)
 
 	hit := int32(0)
 	s := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
@@ -123,14 +123,14 @@ func TestFetchall_malformed(t *testing.T) {
 	cmd.Stderr = os.Stderr
 
 	err = cmd.Run()
-	require.Nil(t, err)
+	require.NoError(t, err)
 
 	require.True(t, atomic.LoadInt32(&hit) >= 2)
 }
 
 func TestFetchall_concurrency(t *testing.T) {
 	binary, err := binCache.GetBinary(fetchallImportPath)
-	require.Nil(t, err)
+	require.NoError(t, err)
 
 	var mu sync.Mutex
 	var callOrder []time.Duration
@@ -140,7 +140,7 @@ func TestFetchall_concurrency(t *testing.T) {
 		require.NotEmpty(t, s)
 
 		d, err := time.ParseDuration(s)
-		require.Nil(t, err)
+		require.NoError(t, err)
 
 		time.Sleep(d)
 
@@ -165,7 +165,7 @@ func TestFetchall_concurrency(t *testing.T) {
 	cmd.Stdout = nil
 	cmd.Stderr = os.Stderr
 
-	require.Nil(t, cmd.Run())
+	require.NoError(t, cmd.Run())
 
 	mu.Lock()
 	defer mu.Unlock()
diff --git a/tools/testtool/commands/test_submission_test.go b/tools/testtool/commands/test_submission_test.go
index 6031b74..8a64296 100644
--- a/tools/testtool/commands/test_submission_test.go
+++ b/tools/testtool/commands/test_submission_test.go
@@ -29,11 +29,11 @@ func listDirs(dir string) ([]string, error) {
 
 func Test_testSubmission_correct(t *testing.T) {
 	testDirs, err := listDirs("../testdata/submissions/correct")
-	require.Nil(t, err)
+	require.NoError(t, err)
 
 	for _, dir := range testDirs {
 		absDir, err := filepath.Abs(dir)
-		require.Nil(t, err)
+		require.NoError(t, err)
 		problem := path.Base(absDir)
 		t.Run(problem, func(t *testing.T) {
 			studentRepo := path.Join(absDir, "student")
@@ -46,11 +46,11 @@ func Test_testSubmission_correct(t *testing.T) {
 
 func Test_testSubmission_incorrect(t *testing.T) {
 	testDirs, err := listDirs("../testdata/submissions/incorrect")
-	require.Nil(t, err)
+	require.NoError(t, err)
 
 	for _, dir := range testDirs {
 		absDir, err := filepath.Abs(dir)
-		require.Nil(t, err)
+		require.NoError(t, err)
 
 		problem := path.Base(absDir)
 		t.Run(problem, func(t *testing.T) {
diff --git a/urlfetch/main_test.go b/urlfetch/main_test.go
index 99b441d..dc5b763 100644
--- a/urlfetch/main_test.go
+++ b/urlfetch/main_test.go
@@ -33,7 +33,7 @@ func TestMain(m *testing.M) {
 
 func TestUrlFetch_valid(t *testing.T) {
 	binary, err := binCache.GetBinary(urlfetchImportPath)
-	require.Nil(t, err)
+	require.NoError(t, err)
 
 	type endpoint string
 	type response string
@@ -91,7 +91,7 @@ func TestUrlFetch_valid(t *testing.T) {
 			cmd.Stderr = os.Stderr
 
 			data, err := cmd.Output()
-			require.Nil(t, err)
+			require.NoError(t, err)
 
 			for _, r := range tc.expected {
 				require.True(t, bytes.Contains(data, []byte(r)),
@@ -104,7 +104,7 @@ func TestUrlFetch_valid(t *testing.T) {
 
 func TestUrlFetch_malformed(t *testing.T) {
 	binary, err := binCache.GetBinary(urlfetchImportPath)
-	require.Nil(t, err)
+	require.NoError(t, err)
 
 	s := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		_, _ = w.Write([]byte("success"))
@@ -141,7 +141,7 @@ func TestUrlFetch_malformed(t *testing.T) {
 
 func TestUrlFetch_order(t *testing.T) {
 	binary, err := binCache.GetBinary(urlfetchImportPath)
-	require.Nil(t, err)
+	require.NoError(t, err)
 
 	mux := http.NewServeMux()
 
@@ -175,7 +175,7 @@ func TestUrlFetch_order(t *testing.T) {
 	cmd.Stdout = nil
 	cmd.Stderr = os.Stderr
 
-	require.Nil(t, cmd.Run())
+	require.NoError(t, cmd.Run())
 
 	mu.Lock()
 	defer mu.Unlock()
diff --git a/wordcount/main_test.go b/wordcount/main_test.go
index e2413dd..179c227 100644
--- a/wordcount/main_test.go
+++ b/wordcount/main_test.go
@@ -33,7 +33,7 @@ func TestMain(m *testing.M) {
 
 func TestWordCount(t *testing.T) {
 	binary, err := binCache.GetBinary(wordcountImportPath)
-	require.Nil(t, err)
+	require.NoError(t, err)
 
 	type counts map[string]int64
 	type files []string
@@ -77,7 +77,7 @@ b`,
 		t.Run(tc.name, func(t *testing.T) {
 			// Create temp directory.
 			testDir, err := ioutil.TempDir("", "wordcount-testdata-")
-			require.Nil(t, err)
+			require.NoError(t, err)
 			defer func() { _ = os.RemoveAll(testDir) }()
 
 			// Create test files in temp directory.
@@ -85,7 +85,7 @@ b`,
 			for _, f := range tc.files {
 				file := path.Join(testDir, testtool.RandomName())
 				err = ioutil.WriteFile(file, []byte(f), 0644)
-				require.Nil(t, err)
+				require.NoError(t, err)
 				files = append(files, file)
 			}
 
@@ -94,11 +94,11 @@ b`,
 			cmd.Stderr = os.Stderr
 
 			output, err := cmd.Output()
-			require.Nil(t, err)
+			require.NoError(t, err)
 
 			// Parse output and compare with an expected one.
 			counts, err := parseStdout(output)
-			require.Nil(t, err)
+			require.NoError(t, err)
 
 			require.True(t, reflect.DeepEqual(tc.expected, counts),
 				fmt.Sprintf("expected: %v; got: %v", tc.expected, counts))