1 files changed, 94 insertions, 0 deletions
diff --git a/internal/ignore/oracle_test.go b/internal/ignore/oracle_test.go
new file mode 100644
index 0000000..a5a589c
--- /dev/null
+++ b/internal/ignore/oracle_test.go
@@ -0,0 +1,94 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package ignore
+
+import (
+	"os"
+	"os/exec"
+	"path/filepath"
+	"sort"
+	"strings"
+	"testing"
+)
+
+var oracleFiles = []string{
+	"a.txt", "b.log", "a1.txt", "abc", ".hidden", "foo.part", "keep.part",
+	"dir/c.txt", "dir/d.log", "dir/.hidden2", "dir/sub/e.txt",
+	"build/out.bin", "src/build/x.go", "doc/readme.md", "doc/sub/readme.md",
+	"deep/a/b/c/file.tmp", "x/z.txt", "x/y/z.txt", "sub/f.txt", "space name.txt",
+	"x]y", "xay", "xby", "a/b", "1.txt", "]a.txt",
+	"a.b", "xyz", "aq", "bq",
+}
+
+var oracleSets = [][]string{
+	{"*.log"}, {"/a.txt"}, {"build/"}, {"doc/*.md"}, {"**/readme.md"},
+	{"deep/**"}, {"x/**/z.txt"}, {"*.part", "!keep.part"}, {".*"},
+	{"a?.txt", "[ab]*.txt"}, {"[!a]*.txt"}, {"dir/", "!dir/c.txt"},
+	{"sub"}, {"space name.txt"}, {"*", "!*.txt"}, {"dir/**/*.txt"},
+	{"x[]a]y"}, {"a[/]b"}, {"[[:digit:]]*.txt"}, {"[!]a]*"},
+	{"a[[:punct:]]b"}, {"x[[:alpha:]]z"}, {"[a\\b]q"},
+}
+
+// TestAgainstGit compares every file and directory of a real tree against
+// `git check-ignore --no-index` for each pattern set.
+func TestAgainstGit(t *testing.T) {
+	if _, err := exec.LookPath("git"); err != nil {
+		t.Skip("git not installed")
+	}
+	root := t.TempDir()
+	t.Setenv("HOME", root)
+	t.Setenv("GIT_CONFIG_GLOBAL", os.DevNull)
+	t.Setenv("GIT_CONFIG_NOSYSTEM", "1")
+	for _, f := range oracleFiles {
+		p := filepath.Join(root, f)
+		if err := os.MkdirAll(filepath.Dir(p), 0o755); err != nil {
+			t.Fatal(err)
+		}
+		if err := os.WriteFile(p, nil, 0o644); err != nil {
+			t.Fatal(err)
+		}
+	}
+	if out, err := exec.Command("git", "-C", root, "init", "-q").CombinedOutput(); err != nil {
+		t.Fatalf("git init: %v %s", err, out)
+	}
+	// every path in the tree, files and directories, relative and slash-separated
+	var paths []string
+	isDir := map[string]bool{}
+	filepath.WalkDir(root, func(p string, d os.DirEntry, err error) error {
+		rel, _ := filepath.Rel(root, p)
+		if rel == "." || rel == ".git" || strings.HasPrefix(rel, ".git"+string(filepath.Separator)) || rel == ".gitignore" {
+			if rel == ".git" {
+				return filepath.SkipDir
+			}
+			return nil
+		}
+		rel = filepath.ToSlash(rel)
+		paths = append(paths, rel)
+		isDir[rel] = d.IsDir()
+		return nil
+	})
+	sort.Strings(paths)
+	for _, set := range oracleSets {
+		if err := os.WriteFile(filepath.Join(root, ".gitignore"), []byte(strings.Join(set, "\n")+"\n"), 0o644); err != nil {
+			t.Fatal(err)
+		}
+		cmd := exec.Command("git", "-C", root, "check-ignore", "--no-index", "--stdin")
+		cmd.Stdin = strings.NewReader(strings.Join(paths, "\n") + "\n")
+		out, _ := cmd.Output() // exit status 1 means "nothing ignored"
+		gitIgnored := map[string]bool{}
+		for _, l := range strings.Split(strings.TrimSpace(string(out)), "\n") {
+			if l != "" {
+				gitIgnored[strings.TrimSuffix(l, "/")] = true
+			}
+		}
+		m, err := New(set)
+		if err != nil {
+			t.Fatalf("New(%q): %v", set, err)
+		}
+		for _, p := range paths {
+			if got := m.Match(p, isDir[p]); got != gitIgnored[p] {
+				t.Errorf("patterns %q, path %q (dir=%v): krino says %v, git says %v", set, p, isDir[p], got, gitIgnored[p])
+			}
+		}
+	}
+}