Add ignorefile read all negative test case

Signed-off-by: Austin Vazquez <[email protected]>

ignorefile/ignorefile_test.go

@@ -1,10 +1,19 @@
 package ignorefile
 
 import (
+	"errors"
 	"strings"
 	"testing"
 )
 
+type emitErrorOnRead struct{}
+
+var errRead = errors.New("read error")
+
+func (r emitErrorOnRead) Read(_ []byte) (int, error) {
+	return 0, errRead
+}
+
 func TestReadAll(t *testing.T) {
 	actual, err := ReadAll(nil)
 	if err != nil {
@@ -14,6 +23,14 @@ func TestReadAll(t *testing.T) {
 		t.Fatalf("Expected to have zero entries, got %d", entries)
 	}
 
+	actual, err = ReadAll(emitErrorOnRead{})
+	if !errors.Is(err, errRead) {
+		t.Fatalf("Expected %v, got %v", errRead, err)
+	}
+	if entries := len(actual); entries != 0 {
+		t.Fatalf("Expected to have zero entries, got %d", entries)
+	}
+
 	const content = `test1
 /test2
 /a/file/here