diff --git a/internal/notifier/matrix_test.go b/internal/notifier/matrix_test.go
index 356812179..6425989c2 100644
--- a/internal/notifier/matrix_test.go
+++ b/internal/notifier/matrix_test.go
@@ -1,6 +1,11 @@
 package notifier
 
 import (
+	"context"
+	"encoding/json"
+	"io"
+	"net/http"
+	"net/http/httptest"
 	"testing"
 	"time"
 
@@ -10,6 +15,106 @@ import (
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 )
 
+func TestNewMatrix(t *testing.T) {
+	t.Run("valid URL", func(t *testing.T) {
+		g := NewWithT(t)
+		matrix, err := NewMatrix("https://matrix.example.com", "token", "!room:example.com", nil)
+		g.Expect(err).ToNot(HaveOccurred())
+		g.Expect(matrix.URL).To(Equal("https://matrix.example.com"))
+		g.Expect(matrix.Token).To(Equal("token"))
+		g.Expect(matrix.RoomId).To(Equal("!room:example.com"))
+	})
+
+	t.Run("invalid URL", func(t *testing.T) {
+		g := NewWithT(t)
+		_, err := NewMatrix("not a url", "token", "!room:example.com", nil)
+		g.Expect(err).To(HaveOccurred())
+		g.Expect(err.Error()).To(ContainSubstring("invalid Matrix homeserver URL"))
+	})
+}
+
+func TestMatrix_Post(t *testing.T) {
+	g := NewWithT(t)
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		g.Expect(r.Method).To(Equal(http.MethodPut))
+		g.Expect(r.Header.Get("Authorization")).To(HavePrefix("Bearer "))
+
+		b, err := io.ReadAll(r.Body)
+		g.Expect(err).ToNot(HaveOccurred())
+		var payload MatrixPayload
+		err = json.Unmarshal(b, &payload)
+		g.Expect(err).ToNot(HaveOccurred())
+
+		g.Expect(payload.MsgType).To(Equal("m.text"))
+		g.Expect(payload.Body).To(ContainSubstring("gitrepository/webapp.gitops-system"))
+		g.Expect(payload.Body).To(ContainSubstring("message"))
+	}))
+	defer ts.Close()
+
+	matrix, err := NewMatrix(ts.URL, "test-token", "!test:example.com", nil)
+	g.Expect(err).ToNot(HaveOccurred())
+
+	err = matrix.Post(context.TODO(), testEvent())
+	g.Expect(err).ToNot(HaveOccurred())
+}
+
+func TestMatrix_PostErrorSeverity(t *testing.T) {
+	g := NewWithT(t)
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		b, err := io.ReadAll(r.Body)
+		g.Expect(err).ToNot(HaveOccurred())
+		var payload MatrixPayload
+		err = json.Unmarshal(b, &payload)
+		g.Expect(err).ToNot(HaveOccurred())
+
+		g.Expect(payload.Body).To(HavePrefix("🚨"))
+	}))
+	defer ts.Close()
+
+	matrix, err := NewMatrix(ts.URL, "test-token", "!test:example.com", nil)
+	g.Expect(err).ToNot(HaveOccurred())
+
+	event := testEvent()
+	event.Severity = eventv1.EventSeverityError
+	err = matrix.Post(context.TODO(), event)
+	g.Expect(err).ToNot(HaveOccurred())
+}
+
+func TestMatrix_PostUsesTransactionID(t *testing.T) {
+	g := NewWithT(t)
+	var requestPaths []string
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		requestPaths = append(requestPaths, r.URL.Path)
+	}))
+	defer ts.Close()
+
+	matrix, err := NewMatrix(ts.URL, "test-token", "!test:example.com", nil)
+	g.Expect(err).ToNot(HaveOccurred())
+
+	err = matrix.Post(context.TODO(), testEvent())
+	g.Expect(err).ToNot(HaveOccurred())
+
+	g.Expect(requestPaths).To(HaveLen(1))
+	g.Expect(requestPaths[0]).To(ContainSubstring("/_matrix/client/r0/rooms/!test:example.com/send/m.room.message/"))
+}
+
+func TestMatrix_PostServerError(t *testing.T) {
+	g := NewWithT(t)
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusInternalServerError)
+	}))
+	defer ts.Close()
+
+	matrix, err := NewMatrix(ts.URL, "test-token", "!test:example.com", nil)
+	g.Expect(err).ToNot(HaveOccurred())
+
+	ctx, cancel := context.WithTimeout(context.Background(), 1*time.Second)
+	defer cancel()
+	err = matrix.Post(ctx, testEvent())
+	g.Expect(err).To(HaveOccurred())
+	g.Expect(err.Error()).To(ContainSubstring("postMessage failed"))
+}
+
 func TestSha1Sum(t *testing.T) {
 	g := NewWithT(t)
 	timestamp, err := time.Parse("Jan 2, 2006 at 3:04pm (WAT)", "Aug 24, 2021 at 4:18pm (WAT)")