diff --git a/testdata/csverror.csv b/testdata/csverror.csv
new file mode 100644
index 0000000..db0fee0
--- /dev/null
+++ b/testdata/csverror.csv
@@ -0,0 +1,3 @@
+2018-01-01T10:00:00.0Z,1.0
+2018-01-02T10:00:00.0Z
+2018-01-02T10:00:00.0Z,2.0
diff --git a/testdata/floaterror.csv b/testdata/floaterror.csv
new file mode 100644
index 0000000..02104bd
--- /dev/null
+++ b/testdata/floaterror.csv
@@ -0,0 +1,3 @@
+2018-01-01T10:00:00.0Z,1.0
+2018-01-02T10:00:00.0Z,str
+2018-01-02T10:00:00.0Z,2.0
diff --git a/timeseries_test.go b/timeseries_test.go
index 0c59493..73da33f 100644
--- a/timeseries_test.go
+++ b/timeseries_test.go
@@ -33,6 +33,14 @@ func TestTimeSeriesRead(t *testing.T) {
 	if record != 1.0 {
 		t.Errorf("unexpected record value %#v", record)
 	}
+
+	testtime = time.Date(2018, 1, 1, 11, 0, 0, 0, time.UTC)
+	record, err = ts.Lookup(testtime)
+	err, ok := err.(InvalidTimestamp)
+	if !ok {
+		t.Fatalf("expected InvalidTimestamp")
+	}
+	err.Error()
 }
 
 func TestTimeSeriesRead_DateOnly(t *testing.T) {
@@ -46,6 +54,42 @@ func TestTimeSeriesRead_DateOnly(t *testing.T) {
 	}
 }
 
+func TestTimeSeriesRead_Error(t *testing.T) {
+	ts := NewTimeSeries()
+	err := ts.Read("testdata/csverror.csv")
+	if err == nil {
+		t.Fatal("expected error")
+	}
+	length := len(ts.records)
+	if length != 1 {
+		t.Errorf("unexpected series length %v", length)
+	}
+}
+
+func TestTimeSeriesRead_DateError(t *testing.T) {
+	ts := NewTimeSeries()
+	err := ts.Read("testdata/dateerror.csv")
+	if err == nil {
+		t.Fatal("expected error")
+	}
+	length := len(ts.records)
+	if length != 1 {
+		t.Errorf("unexpected series length %v", length)
+	}
+}
+
+func TestTimeSeriesRead_FloatError(t *testing.T) {
+	ts := NewTimeSeries()
+	err := ts.Read("testdata/floaterror.csv")
+	if err == nil {
+		t.Fatal("expected error")
+	}
+	length := len(ts.records)
+	if length != 1 {
+		t.Errorf("unexpected series length %v", length)
+	}
+}
+
 func TestTimeSeriesWrite(t *testing.T) {
 	ts := NewTimeSeries()
 	if err := ts.Read("testdata/simple.csv"); err != nil {