diff --git a/msp/msp_test.go b/msp/msp_test.go
index 3eff177..ae500d4 100644
--- a/msp/msp_test.go
+++ b/msp/msp_test.go
@@ -3,17 +3,101 @@ package msp
 import (
 	"fmt"
 	"testing"
+	"time"
 )
 
 //(periods ...Period) (id string, err error) {
 func TestMostSpecificPeriod(t *testing.T) {
+	// use a static timestamp to make sure tests don't fail on slower systems or during a process pause
+	now := time.Now()
 	testCases := []struct {
+		ts      time.Time
 		testID  string
 		result  string
-		Periods []Period
-	}{{testID: "test"}}
+		err     error
+		periods []Period
+	}{{testID: "No choices",
+		ts:      now,
+		result:  "",
+		err:     ErrNoValidPeriods,
+		periods: []Period{}},
+		{testID: "Two Choices, shorter is second",
+			ts:     now,
+			result: "B",
+			err:    nil,
+			periods: []Period{{StartTime: now.Add(-5 * time.Minute),
+				EndTime:    now.Add(time.Minute),
+				Identifier: "A"},
+				{StartTime: now.Add(-2 * time.Minute),
+					EndTime:    now.Add(time.Minute),
+					Identifier: "B"}}},
+		{testID: "Two Choices, one is a year, other a minute",
+			ts:     now,
+			result: "B",
+			err:    nil,
+			periods: []Period{{StartTime: now.Add(-1 * time.Hour * 24 * 365),
+				EndTime:    now.Add(time.Minute),
+				Identifier: "A"},
+				{StartTime: now.Add(-5 * time.Minute),
+					EndTime:    now.Add(time.Minute),
+					Identifier: "B"}}},
+
+		{testID: "Two Choices, shorter is first",
+			ts:     now,
+			result: "A",
+			err:    nil,
+			periods: []Period{{StartTime: now.Add(-2 * time.Minute),
+				EndTime:    now.Add(time.Minute),
+				Identifier: "A"},
+				{StartTime: now.Add(-5 * time.Minute),
+					EndTime:    now.Add(time.Minute),
+					Identifier: "B"}}},
+		{testID: "Two Choices, one in the past",
+			ts:     now,
+			result: "A",
+			err:    nil,
+			periods: []Period{{StartTime: now.Add(-time.Minute),
+				EndTime:    now.Add(time.Minute),
+				Identifier: "A"},
+				{StartTime: now.Add(-2 * time.Minute),
+					EndTime:    now.Add(-time.Minute),
+					Identifier: "B"}}},
+		{testID: "Two Choices, one invalid",
+			ts:     now,
+			result: "B",
+			err:    nil,
+			periods: []Period{{StartTime: now.Add(time.Minute),
+				EndTime:    now.Add(-time.Minute),
+				Identifier: "A"},
+				{StartTime: now.Add(-2 * time.Minute),
+					EndTime:    now.Add(time.Minute),
+					Identifier: "B"}}},
+		{testID: "Two Choices, Identical periods",
+			ts:     now,
+			result: "B",
+			err:    nil,
+			periods: []Period{{StartTime: now.Add(-time.Minute),
+				EndTime:    now.Add(time.Minute),
+				Identifier: "A"},
+				{StartTime: now.Add(-time.Minute),
+					EndTime:    now.Add(time.Minute),
+					Identifier: "B"}}},
+		{testID: "One choice",
+			ts:     now,
+			result: "A",
+			err:    nil,
+			periods: []Period{{StartTime: now.Add(-time.Minute),
+				EndTime:    now.Add(time.Minute),
+				Identifier: "A"}}}}
 	for _, tc := range testCases {
 		t.Run(fmt.Sprintf("%s", tc.testID), func(t *testing.T) {
+			id, err := MostSpecificPeriod(tc.ts, tc.periods...)
+			if id != tc.result {
+				t.Errorf("ID '%s' does not match expected '%s'", id, tc.result)
+			}
+			if err != tc.err {
+				t.Errorf("Error '%v' does not match expected '%v'", err, tc.err)
+			}
 
 		})
 	}