diff --git a/htlcswitch/circuit_test.go b/htlcswitch/circuit_test.go
new file mode 100644
index 00000000..0dad0228
--- /dev/null
+++ b/htlcswitch/circuit_test.go
@@ -0,0 +1,155 @@
+package htlcswitch_test
+
+import (
+	"testing"
+
+	"github.com/lightningnetwork/lnd/htlcswitch"
+	"github.com/lightningnetwork/lnd/lnwire"
+)
+
+func TestCircuitMap(t *testing.T) {
+	t.Parallel()
+
+	var hash1, hash2, hash3 [32]byte
+	hash1[0] = 1
+	hash2[0] = 2
+	hash3[0] = 3
+
+	var (
+		chan1 = lnwire.NewShortChanIDFromInt(1)
+		chan2 = lnwire.NewShortChanIDFromInt(2)
+	)
+
+	circuitMap := htlcswitch.NewCircuitMap()
+
+	circuit := circuitMap.LookupByHTLC(chan1, 0)
+	if circuit != nil {
+		t.Fatalf("LookupByHTLC returned a circuit before any were added: %v",
+			circuit)
+	}
+
+	// Add multiple circuits with same destination channel but different HTLC
+	// IDs and payment hashes.
+	circuitMap.Add(&htlcswitch.PaymentCircuit{
+		PaymentHash: hash1,
+		SrcChanID:   chan2,
+		SrcHTLCID:   1,
+		DestChanID:  chan1,
+		DestHTLCID:  0,
+	})
+
+	circuitMap.Add(&htlcswitch.PaymentCircuit{
+		PaymentHash: hash2,
+		SrcChanID:   chan2,
+		SrcHTLCID:   2,
+		DestChanID:  chan1,
+		DestHTLCID:  1,
+	})
+
+	// Add another circuit with an already-used HTLC ID but different
+	// destination channel.
+	circuitMap.Add(&htlcswitch.PaymentCircuit{
+		PaymentHash: hash3,
+		SrcChanID:   chan1,
+		SrcHTLCID:   2,
+		DestChanID:  chan2,
+		DestHTLCID:  0,
+	})
+
+	circuit = circuitMap.LookupByHTLC(chan1, 0)
+	if circuit == nil {
+		t.Fatal("LookupByHTLC failed to find circuit")
+	}
+	if circuit.PaymentHash != hash1 || circuit.SrcHTLCID != 1 {
+		t.Fatalf("LookupByHTLC found unexpected circuit: %v", circuit)
+	}
+
+	circuit = circuitMap.LookupByHTLC(chan1, 1)
+	if circuit == nil {
+		t.Fatal("LookupByHTLC failed to find circuit")
+	}
+	if circuit.PaymentHash != hash2 || circuit.SrcHTLCID != 2 {
+		t.Fatalf("LookupByHTLC found unexpected circuit: %v", circuit)
+	}
+
+	circuit = circuitMap.LookupByHTLC(chan2, 0)
+	if circuit == nil {
+		t.Fatal("LookupByHTLC failed to find circuit")
+	}
+	if circuit.PaymentHash != hash3 || circuit.SrcHTLCID != 2 {
+		t.Fatalf("LookupByHTLC found unexpected circuit: %v", circuit)
+	}
+
+	// Even though a circuit was added with chan1, HTLC ID 2 as the source, the
+	// lookup should go by destination channel, HTLC ID.
+	circuit = circuitMap.LookupByHTLC(chan1, 2)
+	if circuit != nil {
+		t.Fatalf("LookupByHTLC returned a circuit without being added: %v",
+			circuit)
+	}
+
+	// Add a circuit with a destination channel and payment hash that are
+	// already added but a different HTLC ID.
+	circuitMap.Add(&htlcswitch.PaymentCircuit{
+		PaymentHash: hash1,
+		SrcChanID:   chan2,
+		SrcHTLCID:   3,
+		DestChanID:  chan1,
+		DestHTLCID:  3,
+	})
+
+	circuit = circuitMap.LookupByHTLC(chan1, 3)
+	if circuit == nil {
+		t.Fatal("LookupByHTLC failed to find circuit")
+	}
+	if circuit.PaymentHash != hash1 || circuit.SrcHTLCID != 3 {
+		t.Fatalf("LookupByHTLC found unexpected circuit: %v", circuit)
+	}
+
+	// Check lookups by payment hash.
+	circuits := circuitMap.LookupByPaymentHash(hash1)
+	if len(circuits) != 2 {
+		t.Fatalf("LookupByPaymentHash returned wrong number of circuits for "+
+			"hash1: expected %d, got %d", 2, len(circuits))
+	}
+
+	circuits = circuitMap.LookupByPaymentHash(hash2)
+	if len(circuits) != 1 {
+		t.Fatalf("LookupByPaymentHash returned wrong number of circuits for "+
+			"hash2: expected %d, got %d", 1, len(circuits))
+	}
+
+	// Test removing circuits and the subsequent lookups.
+	err := circuitMap.Remove(chan1, 0)
+	if err != nil {
+		t.Fatalf("Remove returned unexpected error: %v", err)
+	}
+
+	circuits = circuitMap.LookupByPaymentHash(hash1)
+	if len(circuits) != 1 {
+		t.Fatalf("LookupByPaymentHash returned wrong number of circuits for "+
+			"hash1: expecected %d, got %d", 1, len(circuits))
+	}
+	if circuits[0].DestHTLCID != 3 {
+		t.Fatalf("LookupByPaymentHash returned wrong circuit for hash1: %v",
+			circuits[0])
+	}
+
+	// Removing already-removed circuit should return an error.
+	err = circuitMap.Remove(chan1, 0)
+	if err == nil {
+		t.Fatal("Remove did not return expected not found error")
+	}
+
+	// Remove last remaining circuit with payment hash hash1.
+	err = circuitMap.Remove(chan1, 3)
+	if err != nil {
+		t.Fatalf("Remove returned unexpected error: %v", err)
+	}
+
+	circuits = circuitMap.LookupByPaymentHash(hash1)
+	if len(circuits) != 0 {
+		t.Fatalf("LookupByPaymentHash returned wrong number of circuits for "+
+			"hash1: expecected %d, got %d", 0, len(circuits))
+	}
+}