add validation for fromPath

Author: kpechenenko

hw07_file_copying/copy.go

@@ -45,6 +45,9 @@ func Copy(fromPath, toPath string, offset, limit int64) error {
 	if err != nil {
 		return err
 	}
+	if fInfo.IsDir() {
+		return ErrUnsupportedFile
+	}
 	if offset > fInfo.Size() {
 		return ErrOffsetExceedsFileSize
 	}

hw07_file_copying/copy_test.go

@@ -17,6 +17,15 @@ func TestCopy(t *testing.T) {
 		limit         int64
 		err           error
 	}{
+		{
+			name:          "path to source file is directory",
+			fromPath:      "testdata/",
+			toPath:        "testdata/input2.txt",
+			validCopyPath: "testdata/out_offset0_limit0.txt",
+			offset:        0,
+			limit:         0,
+			err:           ErrUnsupportedFile,
+		},
 		{
 			name:          "paths to source and destination files are the same",
 			fromPath:      "testdata/input.txt",