diff --git a/govcr_wb_test.go b/govcr_wb_test.go
index 632f40e..15e42bb 100644
--- a/govcr_wb_test.go
+++ b/govcr_wb_test.go
@@ -19,10 +19,10 @@ import (
 
 func TestRoundTrip_SavesMutatedTracksToCassette(t *testing.T) {
 	const cassetteName = "govcr-fixtures/TestRoundTrip_SavesMutatedCassetteTracks.cassette"
-	_ = os.Remove(cassetteName)
 
 	var testServer *httptest.Server
 
+	// create a test server for the purpose of this test
 	func() {
 		counter := 0
 		testServer = httptest.NewTLSServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
@@ -38,16 +38,22 @@ func TestRoundTrip_SavesMutatedTracksToCassette(t *testing.T) {
 	testServerClient := testServer.Client()
 	testServerClient.Timeout = 3 * time.Second
 
+	// example mutator, mutation is not too intrusive to allow replaying correctly.
+	// for instance, when an Err is injected, the response is set to nil on replay, as per
+	// go's HTTP client design.
 	aMutator := TrackMutator(
 		func(trk *track.Track) {
-			trk.Request.Method = trk.Request.Method + " has been mutated"
+			q := trk.Request.URL.Query()
+			q.Set("mutated_query_key", "this_query_key_has_been_mutated")
+			trk.Request.URL.RawQuery = q.Encode()
 			trk.Response.Status = trk.Response.Status + " has been mutated"
-			trk.ErrType = "ErrType was mutated"
-			trk.ErrMsg = "ErrMsg was mutated"
 		})
 
+	// create a new VCR for the test
 	vcr := NewVCR(WithClient(testServerClient), WithTrackRecordingMutators(aMutator))
 
+	// load a fresh cassette
+	_ = os.Remove(cassetteName)
 	err := vcr.LoadCassette(cassetteName)
 	assert.NoError(t, err)
 	defer func() { _ = os.Remove(cassetteName) }()
@@ -61,15 +67,23 @@ func TestRoundTrip_SavesMutatedTracksToCassette(t *testing.T) {
 	}
 	require.EqualValues(t, expectedStats, actualStats)
 
+	// load the cassette and verify contents has been mutated.
 	err = vcr.LoadCassette(cassetteName)
 	assert.NoError(t, err)
 
 	for trackNum, aTrack := range vcr.vcrTransport().cassette.Tracks {
-		require.EqualValues(t, "GET has been mutated", aTrack.Request.Method, "track #%d", trackNum)
+		require.EqualValues(t, "this_query_key_has_been_mutated", aTrack.Request.URL.Query().Get("mutated_query_key"), "track #%d", trackNum)
 		require.EqualValues(t, "200 OK has been mutated", aTrack.Response.Status, "track #%d", trackNum)
-		require.EqualValues(t, "ErrType was mutated", aTrack.ErrType, "track #%d", trackNum)
-		require.EqualValues(t, "ErrMsg was mutated", aTrack.ErrMsg, "track #%d", trackNum)
 	}
+
+	// 2nd execution of set of calls (replayed)
+	actualStats = replayHTTPCalls_WithMutations_WithSuccess(testServer.URL, vcr, t)
+	expectedStats = stats.Stats{
+		TracksLoaded:   2,
+		TracksRecorded: 0,
+		TracksPlayed:   2,
+	}
+	assert.EqualValues(t, expectedStats, actualStats)
 }
 
 func makeHTTPCalls_WithSuccess(testServerURL string, vcr *ControlPanel, t *testing.T) stats.Stats {
@@ -82,6 +96,49 @@ func makeHTTPCalls_WithSuccess(testServerURL string, vcr *ControlPanel, t *testi
 		resp, err := vcr.Player().Do(req)
 		require.NoError(t, err)
 
+		require.Equal(t, "200 OK", resp.Status)
+		require.Equal(t, http.StatusOK, resp.StatusCode)
+		require.EqualValues(t, strconv.Itoa(38+len(strconv.Itoa(i))), resp.Header.Get("Content-Length"))
+		require.EqualValues(t, "text/plain; charset=utf-8", resp.Header.Get("Content-Type"))
+		require.NotEmpty(t, resp.Header.Get("Date"))
+		require.EqualValues(t, resp.Trailer, http.Header(nil))
+
+		bodyBytes, err := ioutil.ReadAll(resp.Body)
+		require.NoError(t, err)
+		_ = resp.Body.Close()
+		require.Equal(t, fmt.Sprintf("Hello, server responds '%d' to query '%d'", i, i), string(bodyBytes))
+
+		require.Equal(t, int64(38+len(strconv.Itoa(i))), resp.ContentLength)
+		require.NotNil(t, resp.Request)
+		require.NotNil(t, resp.TLS)
+	}
+
+	require.EqualValues(t, 2, vcr.NumberOfTracks())
+
+	actualStats := *vcr.Stats()
+	vcr.EjectCassette()
+
+	return actualStats
+}
+
+func replayHTTPCalls_WithMutations_WithSuccess(testServerURL string, vcr *ControlPanel, t *testing.T) stats.Stats {
+	for i := 1; i <= 2; i++ {
+		req, err := http.NewRequest(http.MethodGet, testServerURL+fmt.Sprintf("?i=%d", i), nil)
+		require.NoError(t, err)
+
+		// manually modify the request inline with the previous mutations that took place.
+		// not doing so would prevent matching our request against the (mutated) cassette.
+		q := req.URL.Query()
+		q.Set("mutated_query_key", "this_query_key_has_been_mutated")
+		req.URL.RawQuery = q.Encode()
+
+		req.Header.Add("header", "value")
+		req.SetBasicAuth("not_a_username", "not_a_password")
+
+		resp, err := vcr.Player().Do(req)
+		require.NoError(t, err)
+
+		require.Equal(t, "200 OK has been mutated", resp.Status)
 		require.Equal(t, http.StatusOK, resp.StatusCode)
 		require.EqualValues(t, strconv.Itoa(38+len(strconv.Itoa(i))), resp.Header.Get("Content-Length"))
 		require.EqualValues(t, "text/plain; charset=utf-8", resp.Header.Get("Content-Type"))
diff --git a/vcrsettings.go b/vcrsettings.go
index bee3fe8..e5bdb13 100644
--- a/vcrsettings.go
+++ b/vcrsettings.go
@@ -14,6 +14,8 @@ type Setting func(vcrConfig *VCRSettings)
 // with the Long Play function enabled.
 // LongPlay simply compresses the contents of the cassette to make
 // it smaller.
+// TODO this is not needed if the LongPlay mode is autosensed from the cassette name
+//      ie if the name ends with '.gz'
 func WithLongPlay() Setting {
 	return func(vcrConfig *VCRSettings) {
 		vcrConfig.longPlay = true