diff --git a/pkg/proxy/intercept/intercept_test.go b/pkg/proxy/intercept/intercept_test.go
index bb5e91d..2652a93 100644
--- a/pkg/proxy/intercept/intercept_test.go
+++ b/pkg/proxy/intercept/intercept_test.go
@@ -129,3 +129,142 @@ func TestRequestModifier(t *testing.T) {
 		}
 	})
 }
+
+func TestResponseModifier(t *testing.T) {
+	t.Parallel()
+
+	t.Run("modify response that's not found", func(t *testing.T) {
+		t.Parallel()
+
+		logger, _ := zap.NewDevelopment()
+		svc := intercept.NewService(intercept.Config{
+			Logger:           logger.Sugar(),
+			RequestsEnabled:  false,
+			ResponsesEnabled: true,
+		})
+
+		reqID := ulid.MustNew(ulid.Timestamp(time.Now()), ulidEntropy)
+
+		err := svc.ModifyResponse(reqID, nil)
+		if !errors.Is(err, intercept.ErrRequestNotFound) {
+			t.Fatalf("expected `intercept.ErrRequestNotFound`, got: %v", err)
+		}
+	})
+
+	t.Run("modify response of request that's done", func(t *testing.T) {
+		t.Parallel()
+
+		logger, _ := zap.NewDevelopment()
+		svc := intercept.NewService(intercept.Config{
+			Logger:           logger.Sugar(),
+			RequestsEnabled:  false,
+			ResponsesEnabled: true,
+		})
+
+		ctx, cancel := context.WithCancel(context.Background())
+		defer cancel()
+
+		req := httptest.NewRequest("GET", "https://example.com/foo", nil)
+		reqID := ulid.MustNew(ulid.Timestamp(time.Now()), ulidEntropy)
+		*req = *req.WithContext(ctx)
+		*req = *req.WithContext(proxy.WithRequestID(req.Context(), reqID))
+
+		res := &http.Response{
+			Request: req,
+			Header:  make(http.Header),
+		}
+		res.Header.Add("X-Foo", "foo")
+
+		var modErr error
+		var wg sync.WaitGroup
+		wg.Add(1)
+
+		next := func(res *http.Response) error { return nil }
+		go func() {
+			defer wg.Done()
+			modErr = svc.ResponseModifier(next)(res)
+		}()
+
+		// Wait shortly, to allow the res modifier goroutine to add `res` to the
+		// array of intercepted responses.
+		time.Sleep(10 * time.Millisecond)
+		cancel()
+
+		modRes := *res
+		modRes.Header = make(http.Header)
+		modRes.Header.Set("X-Foo", "bar")
+
+		err := svc.ModifyResponse(reqID, &modRes)
+		if !errors.Is(err, intercept.ErrRequestDone) {
+			t.Fatalf("expected `intercept.ErrRequestDone`, got: %v", err)
+		}
+
+		wg.Wait()
+
+		if !errors.Is(modErr, context.Canceled) {
+			t.Fatalf("expected `context.Canceled`, got: %v", modErr)
+		}
+	})
+
+	t.Run("modify intercepted response", func(t *testing.T) {
+		t.Parallel()
+
+		req := httptest.NewRequest("GET", "https://example.com/foo", nil)
+		req.Header.Set("X-Foo", "foo")
+
+		reqID := ulid.MustNew(ulid.Timestamp(time.Now()), ulidEntropy)
+		*req = *req.WithContext(proxy.WithRequestID(req.Context(), reqID))
+
+		res := &http.Response{
+			Request: req,
+			Header:  make(http.Header),
+		}
+		res.Header.Add("X-Foo", "foo")
+
+		modRes := *res
+		modRes.Header = make(http.Header)
+		modRes.Header.Set("X-Foo", "bar")
+
+		logger, _ := zap.NewDevelopment()
+		svc := intercept.NewService(intercept.Config{
+			Logger:           logger.Sugar(),
+			RequestsEnabled:  false,
+			ResponsesEnabled: true,
+		})
+
+		var gotHeader string
+
+		var next proxy.ResponseModifyFunc = func(res *http.Response) error {
+			gotHeader = res.Header.Get("X-Foo")
+			return nil
+		}
+
+		var modErr error
+		var wg sync.WaitGroup
+		wg.Add(1)
+
+		go func() {
+			modErr = svc.ResponseModifier(next)(res)
+			wg.Done()
+		}()
+
+		// Wait shortly, to allow the res modifier goroutine to add `req` to the
+		// array of intercepted reqs.
+		time.Sleep(10 * time.Millisecond)
+
+		err := svc.ModifyResponse(reqID, &modRes)
+		if err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+
+		wg.Wait()
+
+		if modErr != nil {
+			t.Fatalf("unexpected error: %v", modErr)
+		}
+
+		if exp := "bar"; exp != gotHeader {
+			t.Fatalf("incorrect modified request header value (expected: %v, got: %v)", exp, gotHeader)
+		}
+	})
+}