Add test for ConsumePartition with OffsetOldest

Also refactor similiar tests and fix docs

consumer_test.go

@@ -20,9 +20,15 @@ func TestConsumerOffsetManual(t *testing.T) {
 	// Given
 	broker0 := NewMockBroker(t, 0)
 
+	manualOffset := int64(1234)
+
 	mockFetchResponse := NewMockFetchResponse(t, 1)
-	for i := 0; i < 10; i++ {
-		mockFetchResponse.SetMessage("my_topic", 0, int64(i+1234), testMsg)
+
+	// skipped because parseRecords(): offset < child.offset
+	mockFetchResponse.SetMessage("my_topic", 0, manualOffset-1, testMsg)
+
+	for i := int64(0); i < 10; i++ {
+		mockFetchResponse.SetMessage("my_topic", 0, i+manualOffset, testMsg)
 	}
 
 	broker0.SetHandlerByMap(map[string]MockResponse{
@@ -41,16 +47,17 @@ func TestConsumerOffsetManual(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	consumer, err := master.ConsumePartition("my_topic", 0, 1234)
+	consumer, err := master.ConsumePartition("my_topic", 0, manualOffset)
 	if err != nil {
 		t.Fatal(err)
 	}
 
-	// Then: messages starting from offset 1234 are consumed.
-	for i := 0; i < 10; i++ {
+	// Then
+
+	for i := int64(0); i < 10; i++ {
 		select {
 		case message := <-consumer.Messages():
-			assertMessageOffset(t, message, int64(i+1234))
+			assertMessageOffset(t, message, i+manualOffset)
 		case err := <-consumer.Errors():
 			t.Error(err)
 		}
@@ -62,23 +69,25 @@ func TestConsumerOffsetManual(t *testing.T) {
 }
 
 // If `OffsetNewest` is passed as the initial offset then the first consumed
-// message is indeed corresponds to the offset that broker claims to be the
+// message indeed corresponds to the offset that broker claims to be the
 // newest in its metadata response.
 func TestConsumerOffsetNewest(t *testing.T) {
 	// Given
+	offsetNewest := int64(10)
+	offsetNewestAfterFetchRequest := int64(50)
 	broker0 := NewMockBroker(t, 0)
 	broker0.SetHandlerByMap(map[string]MockResponse{
 		"MetadataRequest": NewMockMetadataResponse(t).
 			SetBroker(broker0.Addr(), broker0.BrokerID()).
 			SetLeader("my_topic", 0, broker0.BrokerID()),
 		"OffsetRequest": NewMockOffsetResponse(t).
-			SetOffset("my_topic", 0, OffsetNewest, 10).
+			SetOffset("my_topic", 0, OffsetNewest, offsetNewest).
 			SetOffset("my_topic", 0, OffsetOldest, 7),
 		"FetchRequest": NewMockFetchResponse(t, 1).
-			SetMessage("my_topic", 0, 9, testMsg).
+			SetMessage("my_topic", 0, 9, testMsg). // skipped because parseRecords(): offset < child.offset
 			SetMessage("my_topic", 0, 10, testMsg).
 			SetMessage("my_topic", 0, 11, testMsg).
-			SetHighWaterMark("my_topic", 0, 14),
+			SetHighWaterMark("my_topic", 0, offsetNewestAfterFetchRequest),
 	})
 
 	master, err := NewConsumer([]string{broker0.Addr()}, NewTestConfig())
@@ -94,8 +103,53 @@ func TestConsumerOffsetNewest(t *testing.T) {
 
 	// Then
 	assertMessageOffset(t, <-consumer.Messages(), 10)
-	if hwmo := consumer.HighWaterMarkOffset(); hwmo != 14 {
-		t.Errorf("Expected high water mark offset 14, found %d", hwmo)
+	if hwmo := consumer.HighWaterMarkOffset(); hwmo != offsetNewestAfterFetchRequest {
+		t.Errorf("Expected high water mark offset %d, found %d", offsetNewestAfterFetchRequest, hwmo)
+	}
+
+	safeClose(t, consumer)
+	safeClose(t, master)
+	broker0.Close()
+}
+
+// If `OffsetOldest` is passed as the initial offset then the first consumed
+// message is indeed the first available in the partition.
+func TestConsumerOffsetOldest(t *testing.T) {
+	// Given
+	offsetNewest := int64(10)
+	broker0 := NewMockBroker(t, 0)
+	broker0.SetHandlerByMap(map[string]MockResponse{
+		"MetadataRequest": NewMockMetadataResponse(t).
+			SetBroker(broker0.Addr(), broker0.BrokerID()).
+			SetLeader("my_topic", 0, broker0.BrokerID()),
+		"OffsetRequest": NewMockOffsetResponse(t).
+			SetOffset("my_topic", 0, OffsetNewest, offsetNewest).
+			SetOffset("my_topic", 0, OffsetOldest, 7),
+		"FetchRequest": NewMockFetchResponse(t, 1).
+			// skipped because parseRecords(): offset < child.offset
+			SetMessage("my_topic", 0, 6, testMsg).
+			// these will get to the Messages() channel
+			SetMessage("my_topic", 0, 7, testMsg).
+			SetMessage("my_topic", 0, 8, testMsg).
+			SetMessage("my_topic", 0, 9, testMsg).
+			SetHighWaterMark("my_topic", 0, offsetNewest),
+	})
+
+	master, err := NewConsumer([]string{broker0.Addr()}, NewTestConfig())
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// When
+	consumer, err := master.ConsumePartition("my_topic", 0, OffsetOldest)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Then
+	assertMessageOffset(t, <-consumer.Messages(), int64(7))
+	if hwmo := consumer.HighWaterMarkOffset(); hwmo != offsetNewest {
+		t.Errorf("Expected high water mark offset %d, found %d", offsetNewest, hwmo)
 	}
 
 	safeClose(t, consumer)