Projection: excluded and included fields

tests/ferret/core_test.go

@@ -54,7 +54,6 @@ func TestCore(t *testing.T) {
 			var writeErr mongo.BulkWriteException
 			assert.ErrorAs(t, err, &writeErr)
 			assert.True(t, writeErr.HasErrorCode(11000))
-
 			cursor, err := collection.Find(ctx, bson.D{}, options.Find().SetSort(bson.D{{"_id", 1}}))
 			require.NoError(t, err)
 			require.NoError(t, cursor.All(ctx, &docs))
@@ -153,6 +152,8 @@ func TestCore(t *testing.T) {
 		testCases := []struct {
 			name string // TODO move to map key
 			q    bson.D
+			o    *options.FindOptions
+			v    bson.D
 			IDs  []string
 			err  error
 		}{
@@ -217,6 +218,45 @@ func TestCore(t *testing.T) {
 			// documents
 			// TODO
 
+			// projection
+			{
+				name: "ProjectionInclusion",
+				q: bson.D{
+					{"_id", "double"},
+				},
+				o: options.Find().SetProjection(bson.D{{"value", int32(11)}}),
+				v: bson.D{
+					{"_id", "double"},
+					{"value", 42.13},
+				},
+				IDs: []string{"double"},
+			},
+			{
+				name: "ProjectionExclusion",
+				q: bson.D{
+					{"_id", "double"},
+				},
+				o: options.Find().SetProjection(bson.D{{"value", false}}),
+				v: bson.D{
+					{"_id", "double"},
+				},
+				IDs: []string{"double"},
+			},
+			{
+				name: "ProjectionBothError",
+				q: bson.D{
+					{"_id", "document-diverse"},
+				},
+				o: options.Find().SetProjection(bson.D{
+					{"document_id", false},
+					{"array", true},
+				}),
+				err: mongo.CommandError{
+					Code:    2,
+					Name:    "BadValue",
+					Message: `projection must contain only inclusions or exclusions`,
+				},
+			},
 			// arrays
 			// $size
 			{
@@ -314,7 +354,13 @@ func TestCore(t *testing.T) {
 					t.Fatal("exactly one of IDs or err must be set")
 				}
 
-				cursor, err := collection.Find(ctx, tc.q, options.Find().SetSort(bson.D{{"value", 1}}))
+				var cursor *mongo.Cursor
+				var err error
+				opts := options.Find().SetSort(bson.D{{"value", 1}})
+				if tc.o != nil {
+					opts = tc.o
+				}
+				cursor, err = collection.Find(ctx, tc.q, opts)
 
 				if tc.err != nil {
 					require.Error(t, err)
@@ -326,10 +372,15 @@ func TestCore(t *testing.T) {
 				require.NotNil(t, cursor)
 
 				var expected []bson.D
+
 				for _, id := range tc.IDs {
 					v, ok := data[id]
 					require.True(t, ok)
-					expected = append(expected, bson.D{{"_id", id}, {"value", v}})
+					if tc.v != nil {
+						expected = append(expected, tc.v)
+					} else {
+						expected = append(expected, bson.D{{"_id", id}, {"value", v}})
+					}
 				}
 
 				var actual []bson.D