test: cover clipboard Validate/DryRun branches and testing helper

Adds unit tests for the clipboard-related Validate/DryRun paths that
Codecov patch-coverage was flagging as uncovered:

- Validate error when neither --file nor --from-clipboard is supplied
- Validate error when both are supplied (mutual exclusion)
- DryRun output contains <clipboard image> placeholder
- Self-test for TestNewRuntimeContextForAPI so shortcuts/common
  sees coverage for the new helper (not just shortcuts/doc)

shortcuts/common/testing_test.go

@@ -0,0 +1,42 @@
+// Copyright (c) 2026 Lark Technologies Pte. Ltd.
+// SPDX-License-Identifier: MIT
+
+package common
+
+import (
+	"context"
+	"testing"
+
+	"github.com/spf13/cobra"
+
+	"github.com/larksuite/cli/internal/cmdutil"
+	"github.com/larksuite/cli/internal/core"
+)
+
+func TestTestNewRuntimeContextForAPIWiresFields(t *testing.T) {
+	t.Setenv("LARKSUITE_CLI_CONFIG_DIR", t.TempDir())
+	cfg := &core.CliConfig{AppID: "self-test-app", AppSecret: "secret", Brand: core.BrandFeishu}
+	f, _, _, _ := cmdutil.TestFactory(t, cfg)
+	cmd := &cobra.Command{Use: "testing-helper"}
+
+	ctx := context.Background()
+	rctx := TestNewRuntimeContextForAPI(ctx, cmd, cfg, f)
+	if rctx == nil {
+		t.Fatal("TestNewRuntimeContextForAPI returned nil")
+	}
+	if rctx.Cmd != cmd {
+		t.Errorf("Cmd not wired")
+	}
+	if rctx.Config != cfg {
+		t.Errorf("Config not wired")
+	}
+	if rctx.Factory != f {
+		t.Errorf("Factory not wired")
+	}
+	if !rctx.resolvedAs.IsBot() {
+		t.Errorf("resolvedAs not set to bot, got %q", rctx.resolvedAs)
+	}
+	if rctx.Ctx() != ctx {
+		t.Errorf("ctx not wired")
+	}
+}

shortcuts/doc/doc_media_test.go

@@ -75,6 +75,62 @@ func TestDocMediaInsertRejectsOldDocURL(t *testing.T) {
 	}
 }
 
+func TestDocMediaInsertValidateRequiresFileOrClipboard(t *testing.T) {
+	f, _, _, _ := cmdutil.TestFactory(t, docsTestConfigWithAppID("docs-test-app"))
+
+	err := mountAndRunDocs(t, DocMediaInsert, []string{
+		"+media-insert",
+		"--doc", "https://example.larksuite.com/docx/doxcnXXXXXXXXXXXXXXXXXX",
+		"--dry-run",
+		"--as", "bot",
+	}, f, nil)
+	if err == nil {
+		t.Fatal("expected validation error, got nil")
+	}
+	if !strings.Contains(err.Error(), "one of --file or --from-clipboard is required") {
+		t.Fatalf("unexpected error: %v", err)
+	}
+}
+
+func TestDocMediaInsertValidateRejectsFileAndClipboardTogether(t *testing.T) {
+	f, _, _, _ := cmdutil.TestFactory(t, docsTestConfigWithAppID("docs-test-app"))
+
+	err := mountAndRunDocs(t, DocMediaInsert, []string{
+		"+media-insert",
+		"--doc", "https://example.larksuite.com/docx/doxcnXXXXXXXXXXXXXXXXXX",
+		"--file", "dummy.png",
+		"--from-clipboard",
+		"--dry-run",
+		"--as", "bot",
+	}, f, nil)
+	if err == nil {
+		t.Fatal("expected mutual-exclusion error, got nil")
+	}
+	if !strings.Contains(err.Error(), "mutually exclusive") {
+		t.Fatalf("unexpected error: %v", err)
+	}
+}
+
+func TestDocMediaInsertDryRunWithClipboardUsesPlaceholder(t *testing.T) {
+	f, stdout, _, _ := cmdutil.TestFactory(t, docsTestConfigWithAppID("docs-test-app"))
+
+	err := mountAndRunDocs(t, DocMediaInsert, []string{
+		"+media-insert",
+		"--doc", "https://example.larksuite.com/docx/doxcnXXXXXXXXXXXXXXXXXX",
+		"--from-clipboard",
+		"--dry-run",
+		"--as", "bot",
+	}, f, stdout)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	// JSON output escapes "<" and ">" as \u003c / \u003e by default.
+	out := stdout.String()
+	if !strings.Contains(out, `\u003cclipboard image\u003e`) && !strings.Contains(out, "<clipboard image>") {
+		t.Fatalf("dry-run output missing <clipboard image> placeholder: %s", out)
+	}
+}
+
 func TestDocMediaInsertDryRunWikiAddsResolveStep(t *testing.T) {
 	f, stdout, _, _ := cmdutil.TestFactory(t, docsTestConfigWithAppID("docs-test-app"))