chore: import upstream snapshot with attribution

internal/diff/diff_extra_test.go

@@ -0,0 +1,182 @@
+package diff
+
+import (
+	"strings"
+	"testing"
+)
+
+// --- splitLines ---
+
+func TestSplitLinesEmpty(t *testing.T) {
+	lines, eol := splitLines("")
+	if len(lines) != 0 {
+		t.Errorf("empty: got %d lines", len(lines))
+	}
+	if !eol {
+		t.Error("empty should report endsWithNewline=true")
+	}
+}
+
+func TestSplitLinesNoTrailingNewline(t *testing.T) {
+	lines, eol := splitLines("a\nb")
+	if len(lines) != 2 {
+		t.Errorf("got %d lines", len(lines))
+	}
+	if lines[0] != "a" || lines[1] != "b" {
+		t.Errorf("lines = %v", lines)
+	}
+	if eol {
+		t.Error("should report no trailing newline")
+	}
+}
+
+func TestSplitLinesTrailingNewline(t *testing.T) {
+	lines, eol := splitLines("a\nb\n")
+	if len(lines) != 2 {
+		t.Errorf("got %d lines", len(lines))
+	}
+	if !eol {
+		t.Error("should report trailing newline")
+	}
+}
+
+func TestSplitLinesSingleLine(t *testing.T) {
+	lines, eol := splitLines("hello")
+	if len(lines) != 1 || lines[0] != "hello" {
+		t.Errorf("lines = %v", lines)
+	}
+	if eol {
+		t.Error("single line without newline should report false")
+	}
+}
+
+func TestSplitLinesSingleLineWithNewline(t *testing.T) {
+	lines, eol := splitLines("hello\n")
+	if len(lines) != 1 || lines[0] != "hello" {
+		t.Errorf("lines = %v", lines)
+	}
+	if !eol {
+		t.Error("single line with newline should report true")
+	}
+}
+
+// --- isBinary ---
+
+func TestIsBinaryEmpty(t *testing.T) {
+	if isBinary("") {
+		t.Error("empty string is not binary")
+	}
+}
+
+func TestIsBinaryText(t *testing.T) {
+	if isBinary("hello world\nline 2") {
+		t.Error("plain text is not binary")
+	}
+}
+
+func TestIsBinaryNUL(t *testing.T) {
+	if !isBinary("hello\x00world") {
+		t.Error("string with NUL should be binary")
+	}
+}
+
+func TestIsBinaryNULAtEnd(t *testing.T) {
+	if !isBinary("hello\x00") {
+		t.Error("NUL at end should be binary")
+	}
+}
+
+// --- Build edge cases ---
+
+func TestBuildBothEmpty(t *testing.T) {
+	c := Build("empty.txt", "", "", Modify)
+	if c.Diff != "" || c.Added != 0 || c.Removed != 0 {
+		t.Errorf("both empty should be no-op: %+v", c)
+	}
+}
+
+func TestBuildEmptyOldNonEmptyNew(t *testing.T) {
+	c := Build("new.txt", "", "line1\nline2\n", Create)
+	if c.Added != 2 || c.Removed != 0 {
+		t.Errorf("added/removed = %d/%d", c.Added, c.Removed)
+	}
+	if c.Kind != Create {
+		t.Errorf("kind = %q", c.Kind)
+	}
+}
+
+func TestBuildNonEmptyOldEmptyNew(t *testing.T) {
+	c := Build("del.txt", "line1\nline2\n", "", Delete)
+	if c.Added != 0 || c.Removed != 2 {
+		t.Errorf("added/removed = %d/%d", c.Added, c.Removed)
+	}
+}
+
+func TestBuildCRLF(t *testing.T) {
+	old := "line1\r\nline2\r\n"
+	neu := "line1\r\nLINE2\r\n"
+	c := Build("crlf.txt", old, neu, Modify)
+	// CRLF should be handled (split on \n, \r stays in line content).
+	if c.Added != 1 || c.Removed != 1 {
+		t.Errorf("added/removed = %d/%d, want 1/1", c.Added, c.Removed)
+	}
+}
+
+func TestBuildWhitespaceOnly(t *testing.T) {
+	old := "a\tb\n"
+	neu := "a  b\n"
+	c := Build("ws.txt", old, neu, Modify)
+	if c.Added != 1 || c.Removed != 1 {
+		t.Errorf("added/removed = %d/%d", c.Added, c.Removed)
+	}
+}
+
+func TestBuildLargeFile(t *testing.T) {
+	// Build a large file with one changed line in the middle.
+	var oldB, newB strings.Builder
+	for i := 0; i < 1000; i++ {
+		oldB.WriteString("line\n")
+		if i == 500 {
+			newB.WriteString("CHANGED\n")
+		} else {
+			newB.WriteString("line\n")
+		}
+	}
+	c := Build("large.txt", oldB.String(), newB.String(), Modify)
+	if c.Added != 1 || c.Removed != 1 {
+		t.Errorf("added/removed = %d/%d, want 1/1", c.Added, c.Removed)
+	}
+}
+
+// --- Kind constants ---
+
+func TestKindConstants(t *testing.T) {
+	if Create != "create" {
+		t.Errorf("Create = %q", Create)
+	}
+	if Modify != "modify" {
+		t.Errorf("Modify = %q", Modify)
+	}
+	if Delete != "delete" {
+		t.Errorf("Delete = %q", Delete)
+	}
+}
+
+// --- itoa ---
+
+func TestItoa(t *testing.T) {
+	cases := []struct {
+		n    int
+		want string
+	}{
+		{0, "0"},
+		{1, "1"},
+		{42, "42"},
+		{1000, "1000"},
+	}
+	for _, c := range cases {
+		if got := itoa(c.n); got != c.want {
+			t.Errorf("itoa(%d) = %q, want %q", c.n, got, c.want)
+		}
+	}
+}