1 files changed, 83 insertions, 0 deletions
diff --git a/internal/lsp/extract_range_text_test.go b/internal/lsp/extract_range_text_test.go
new file mode 100644
index 0000000..1fe29ae
--- /dev/null
+++ b/internal/lsp/extract_range_text_test.go
@@ -0,0 +1,83 @@
+package lsp
+
+import "testing"
+
+func TestExtractRangeText_NilDocument(t *testing.T) {
+	got := extractRangeText(nil, Range{})
+	if got != "" {
+		t.Fatalf("expected empty, got %q", got)
+	}
+}
+
+func TestExtractRangeText_EmptyLines(t *testing.T) {
+	d := &document{lines: []string{}}
+	got := extractRangeText(d, Range{Start: Position{0, 0}, End: Position{0, 5}})
+	if got != "" {
+		t.Fatalf("expected empty, got %q", got)
+	}
+}
+
+func TestExtractRangeText_NegativeStartLine(t *testing.T) {
+	d := &document{lines: []string{"hello"}}
+	got := extractRangeText(d, Range{Start: Position{-1, 0}, End: Position{0, 3}})
+	if got != "" {
+		t.Fatalf("expected empty, got %q", got)
+	}
+}
+
+func TestExtractRangeText_NegativeEndLine(t *testing.T) {
+	d := &document{lines: []string{"hello"}}
+	got := extractRangeText(d, Range{Start: Position{0, 0}, End: Position{-1, 3}})
+	if got != "" {
+		t.Fatalf("expected empty, got %q", got)
+	}
+}
+
+func TestExtractRangeText_StartLineBeyondEnd(t *testing.T) {
+	d := &document{lines: []string{"hello", "world"}}
+	got := extractRangeText(d, Range{Start: Position{5, 0}, End: Position{6, 0}})
+	if got != "" {
+		t.Fatalf("expected empty, got %q", got)
+	}
+}
+
+func TestExtractRangeText_EndLineBeyondEnd(t *testing.T) {
+	// End line is clamped to the last valid line.
+	d := &document{lines: []string{"hello", "world"}}
+	got := extractRangeText(d, Range{Start: Position{0, 0}, End: Position{10, 5}})
+	if got != "hello\nworld" {
+		t.Fatalf("expected clamped result, got %q", got)
+	}
+}
+
+func TestExtractRangeText_StartAfterEnd(t *testing.T) {
+	d := &document{lines: []string{"aaa", "bbb"}}
+	got := extractRangeText(d, Range{Start: Position{1, 0}, End: Position{0, 2}})
+	if got != "" {
+		t.Fatalf("expected empty, got %q", got)
+	}
+}
+
+func TestExtractRangeText_SingleLine(t *testing.T) {
+	d := &document{lines: []string{"hello world"}}
+	got := extractRangeText(d, Range{Start: Position{0, 6}, End: Position{0, 11}})
+	if got != "world" {
+		t.Fatalf("expected %q, got %q", "world", got)
+	}
+}
+
+func TestExtractRangeText_SingleLineNegativeChar(t *testing.T) {
+	d := &document{lines: []string{"hello"}}
+	got := extractRangeText(d, Range{Start: Position{0, -3}, End: Position{0, 3}})
+	if got != "hel" {
+		t.Fatalf("expected %q, got %q", "hel", got)
+	}
+}
+
+func TestExtractRangeText_MultiLine(t *testing.T) {
+	d := &document{lines: []string{"aaa", "bbb", "ccc"}}
+	got := extractRangeText(d, Range{Start: Position{0, 1}, End: Position{2, 2}})
+	if got != "aa\nbbb\ncc" {
+		t.Fatalf("expected %q, got %q", "aa\nbbb\ncc", got)
+	}
+}