add tests for creating reader with broken file

this test illustrates the need for New(Generic)ReaderWithError

file_test.go

@@ -15,6 +15,10 @@ var testdataFiles []string
 func init() {
 	entries, _ := os.ReadDir("testdata")
 	for _, e := range entries {
+		if e.IsDir() {
+			continue
+		}
+
 		testdataFiles = append(testdataFiles, filepath.Join("testdata", e.Name()))
 	}
 }

reader_go18_test.go

@@ -8,6 +8,8 @@ import (
 	"fmt"
 	"io"
 	"math/rand"
+	"os"
+	"path/filepath"
 	"reflect"
 	"testing"
 
@@ -161,3 +163,19 @@ func benchmarkGenericReader[Row generator[Row]](b *testing.B) {
 		})
 	})
 }
+
+func TestGenericReaderFailure(t *testing.T) {
+	invalidFileName := filepath.Join("testdata", "invalid", "not_enough_columns.invalid.parquet")
+
+	file, err := os.Open(invalidFileName)
+	if err != nil {
+		t.Fatalf("failed to read %q: %s", invalidFileName, err.Error())
+	}
+
+	defer file.Close()
+
+	_, err = parquet.NewGenericReaderWithError[map[string]any](file)
+	if err == nil {
+		t.Fatalf("expected an error when trying to open invalid file %q, but didn't get one", invalidFileName)
+	}
+}

reader_test.go

@@ -6,6 +6,8 @@ import (
 	"io"
 	"math"
 	"math/rand"
+	"os"
+	"path/filepath"
 	"reflect"
 	"testing"
 
@@ -535,3 +537,19 @@ func TestSeekToRowDictReadMultiplePages(t *testing.T) {
 		t.Fatalf("read != write")
 	}
 }
+
+func TestReaderFailure(t *testing.T) {
+	invalidFileName := filepath.Join("testdata", "invalid", "not_enough_columns.invalid.parquet")
+
+	file, err := os.Open(invalidFileName)
+	if err != nil {
+		t.Fatalf("failed to read %q: %s", invalidFileName, err.Error())
+	}
+
+	defer file.Close()
+
+	_, err = parquet.NewReaderWithError(file)
+	if err == nil {
+		t.Fatalf("expected an error when trying to open invalid file %q, but didn't get one", invalidFileName)
+	}
+}