test(testrun): exact-output tests for progressHandler line format

internal/testrun/progress_test.go

@@ -0,0 +1,53 @@
+package testrun
+
+import (
+	"bytes"
+	"context"
+	"log/slog"
+	"testing"
+	"time"
+)
+
+func TestProgressHandler_LineFormat(t *testing.T) {
+	tests := []struct {
+		name  string
+		level slog.Level
+		msg   string
+		attrs []slog.Attr
+		want  string
+	}{
+		{"info has no level prefix", slog.LevelInfo, "running", nil, "running\n"},
+		{"warn prefixes lowercased level", slog.LevelWarn, "slow", nil, "warn: slow\n"},
+		{"error prefixes lowercased level", slog.LevelError, "boom", nil, "error: boom\n"},
+		{
+			"string attr is quoted",
+			slog.LevelInfo, "step", []slog.Attr{slog.String("name", "tap home")},
+			"step name=\"tap home\"\n",
+		},
+		{
+			"non-string attr renders bare",
+			slog.LevelInfo, "step", []slog.Attr{slog.Int("seed", 42)},
+			"step seed=42\n",
+		},
+		{
+			"attrs render in order",
+			slog.LevelInfo, "step",
+			[]slog.Attr{slog.Int("n", 1), slog.String("k", "v")},
+			"step n=1 k=\"v\"\n",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var buf bytes.Buffer
+			h := &progressHandler{writer: &buf, level: slog.LevelInfo}
+			record := slog.NewRecord(time.Time{}, tt.level, tt.msg, 0)
+			record.AddAttrs(tt.attrs...)
+			if err := h.Handle(context.Background(), record); err != nil {
+				t.Fatal(err)
+			}
+			if got := buf.String(); got != tt.want {
+				t.Fatalf("got %q, want %q", got, tt.want)
+			}
+		})
+	}
+}