diff --git a/config/config_test.go b/config/config_test.go
new file mode 100644
index 0000000..ea84b43
--- /dev/null
+++ b/config/config_test.go
@@ -0,0 +1,15 @@
+package config
+
+import (
+	"testing"
+)
+
+// Verify that the sample config in config/config.json can be read to a config struct
+// and passes the validation
+func TestSampleConfig(t *testing.T) {
+	var conf Config
+	err := ReadConfigFile("config.json", &conf)
+	if err != nil {
+		t.Errorf("Unable to use sample config file: %s", err)
+	}
+}
diff --git a/models/date.go b/models/date.go
index 23462b0..61ce6a3 100644
--- a/models/date.go
+++ b/models/date.go
@@ -59,7 +59,7 @@ func GetEndDate(date Date, duration int, ignoreWeek bool) Date {
 		endDate = Date{date.Week, date.Day, date.Hour, date.Minute}
 	}
 	endDate.Day = (endDate.Day + (endDate.Hour*60+endDate.Minute+duration)/(60*24)) % 7
-	endDate.Hour = endDate.Hour + (endDate.Minute+duration)/60
+	endDate.Hour = (endDate.Hour + (endDate.Minute+duration)/60) % 24
 	endDate.Minute = (endDate.Minute + duration) % 60
 	return endDate
 }
diff --git a/models/date_test.go b/models/date_test.go
new file mode 100644
index 0000000..43c54bd
--- /dev/null
+++ b/models/date_test.go
@@ -0,0 +1,62 @@
+package models
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestEndDate(t *testing.T) {
+	testCases := []struct {
+		startDate Date
+		duration  int
+		endDate   Date
+	}{
+		{Date{Week: 0, Day: 0, Hour: 8, Minute: 0}, 10, Date{Week: 0, Day: 0, Hour: 8, Minute: 10}},
+		{Date{Week: 0, Day: 0, Hour: 8, Minute: 0}, 90, Date{Week: 0, Day: 0, Hour: 9, Minute: 30}},   // More than one hour
+		{Date{Week: 0, Day: 0, Hour: 8, Minute: 0}, 130, Date{Week: 0, Day: 0, Hour: 10, Minute: 10}}, // More than two hours
+		{Date{Week: 0, Day: 0, Hour: 8, Minute: 15}, 90, Date{Week: 0, Day: 0, Hour: 9, Minute: 45}},  // More than one hour and start not 0
+		{Date{Week: 0, Day: 0, Hour: 23, Minute: 15}, 90, Date{Week: 0, Day: 1, Hour: 0, Minute: 45}}, // More than one day
+	}
+	for _, tc := range testCases {
+		t.Run(fmt.Sprintf("%d:%d, Dauer %d", tc.startDate.Hour, tc.startDate.Minute, tc.duration), func(t *testing.T) {
+			got := GetEndDate(tc.startDate, tc.duration, false)
+			if got != tc.endDate {
+				t.Errorf("got %v; want %v", got, tc.endDate)
+			}
+		})
+	}
+}
+
+func TestDateLess(t *testing.T) {
+	testCases := []struct {
+		name   string
+		first  Date
+		second Date
+		less   bool
+	}{
+		{"earlier day",
+			Date{Week: 0, Day: 1, Hour: 8, Minute: 10}, Date{Week: 0, Day: 0, Hour: 7, Minute: 10}, false},
+		{"earlier hour",
+			Date{Week: 0, Day: 1, Hour: 8, Minute: 10}, Date{Week: 0, Day: 1, Hour: 7, Minute: 10}, false},
+		{"earlier minute",
+			Date{Week: 0, Day: 1, Hour: 8, Minute: 10}, Date{Week: 0, Day: 1, Hour: 8, Minute: 0}, false},
+		{"same date",
+			Date{Week: 0, Day: 1, Hour: 8, Minute: 10}, Date{Week: 0, Day: 1, Hour: 8, Minute: 10}, false},
+		{"later minute",
+			Date{Week: 0, Day: 1, Hour: 8, Minute: 10}, Date{Week: 0, Day: 1, Hour: 8, Minute: 20}, true},
+		{"later hour",
+			Date{Week: 0, Day: 1, Hour: 8, Minute: 10}, Date{Week: 0, Day: 1, Hour: 9, Minute: 10}, true},
+		{"later day",
+			Date{Week: 0, Day: 1, Hour: 8, Minute: 10}, Date{Week: 0, Day: 2, Hour: 8, Minute: 10}, true},
+		{"week should not matter",
+			Date{Week: 1, Day: 1, Hour: 8, Minute: 10}, Date{Week: 0, Day: 1, Hour: 9, Minute: 30}, true},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			got := DateLess(tc.first, tc.second)
+			if got != tc.less {
+				t.Errorf("got %t; want %t", got, tc.less)
+			}
+		})
+	}
+}