diff --git a/pkg/extension/server_test.go b/pkg/extension/server_test.go
index 3f8e408b21a25159cb94ea7527d899150354f278..bee68b1a8e3f8ca90beae259ceda2a933e3f6b3e 100644
--- a/pkg/extension/server_test.go
+++ b/pkg/extension/server_test.go
@@ -121,21 +121,31 @@ func TestServer_Action(t *testing.T) {
 		services map[string]Extension
 		in       *ActionRequest
 		want     *ActionResponse
-		wantErr  assert.ErrorAssertionFunc
+		wantErr  string
 	}{
 		{
-			name:     "OK (grpc)",
+			name:     "GRPC",
 			services: map[string]Extension{"test-extension": getDummyExtension("test-extension")},
 			in: &ActionRequest{
 				Action:  "grpc:///test-extension/test-action",
 				SpaceId: "sp",
 				EnvId:   "env",
 			},
+			want: &ActionResponse{State: ResponseDone},
+		},
+		{
+			name:     "invalid schema",
+			services: map[string]Extension{"test-extension": getDummyExtension("test-extension")},
+			in: &ActionRequest{
+				Action:  "some:///space/env/coll",
+				SpaceId: "sp",
+				EnvId:   "env",
+			},
 			want:    &ActionResponse{State: ResponseDone},
-			wantErr: assert.NoError,
+			wantErr: "extension ID required",
 		},
 		{
-			name:     "OK (deprecated call)",
+			name:     "Deprecated call",
 			services: map[string]Extension{"test-extension": getDummyExtension("test-extension")},
 			in: &ActionRequest{
 				Action:    "test-action",
@@ -143,11 +153,10 @@ func TestServer_Action(t *testing.T) {
 				EnvId:     "env",
 				Extension: "test-extension",
 			},
-			want:    &ActionResponse{State: ResponseDone},
-			wantErr: assert.NoError,
+			want: &ActionResponse{State: ResponseDone},
 		},
 		{
-			name:     "Error (unknown extension)",
+			name:     "unknown extension",
 			services: map[string]Extension{"test-extension": getDummyExtension("test-extension")},
 			in: &ActionRequest{
 				Action:  "grpc:///test-extension-2/test-action",
@@ -155,10 +164,10 @@ func TestServer_Action(t *testing.T) {
 				EnvId:   "env",
 			},
 			want:    nil,
-			wantErr: assert.Error,
+			wantErr: ErrUnknownExtension.Error(),
 		},
 		{
-			name:     "Error (deprecated call, no extension)",
+			name:     "Deprecated call, without extension",
 			services: map[string]Extension{"test-extension": getDummyExtension("test-extension")},
 			in: &ActionRequest{
 				Action:  "test-action",
@@ -166,17 +175,17 @@ func TestServer_Action(t *testing.T) {
 				EnvId:   "env",
 			},
 			want:    nil,
-			wantErr: assert.Error,
+			wantErr: "extension ID required",
 		},
 		{
-			name:     "Error (deprecated call, no action and extension)",
+			name:     "Deprecated call, without action and extension)",
 			services: map[string]Extension{"test-extension": getDummyExtension("test-extension")},
 			in: &ActionRequest{
 				SpaceId: "sp",
 				EnvId:   "env",
 			},
 			want:    nil,
-			wantErr: assert.Error,
+			wantErr: "extension ID required",
 		},
 	}
 	for _, tt := range tests {
@@ -186,7 +195,8 @@ func TestServer_Action(t *testing.T) {
 				services: tt.services,
 			}
 			got, err := srv.Action(context.Background(), tt.in)
-			if !tt.wantErr(t, err, fmt.Sprintf("Action(%v)", tt.in)) {
+			if tt.wantErr != "" {
+				assert.EqualErrorf(t, err, tt.wantErr, fmt.Sprintf("Action(%v)", tt.in))
 				return
 			}
 			assert.Equalf(t, tt.want, got, "Action(%v)", tt.in)