cue/load: create test data with broken cue dynamically

In https://cuelang.org/cl/1193030, multiple cue files were added in
order to test that load.Instances returns build instances sorted by
directory and package name.
Each cue file belongs to a different package, causing commands like
`cue vet ./...` to fail with the following error:

    found packages "a" (a.cue) and "b" (b.cue) in
    "cue/load/testdata/testsort"

To resolve this these cue files are created dynamically as part of the
test, instead of being stored statically on disk.

Change-Id: I94661c5446183ad300b37ddf46312821dbd8a66b
Signed-off-by: Noam Dolovich <[email protected]>
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1195592
TryBot-Result: CUEcueckoo <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>
Reviewed-by: Daniel Martí <[email protected]>

cue/load/loader_test.go

@@ -16,6 +16,7 @@ package load
 
 import (
 	"bytes"
+	"fmt"
 	"os"
 	"path/filepath"
 	"strings"
@@ -467,22 +468,34 @@ func TestOverlays(t *testing.T) {
 }
 
 func TestLoadOrder(t *testing.T) {
-	testDataDir := testdata("testsort")
+	testDir := t.TempDir()
+	letters := "abcdefghij"
+
+	for _, c := range letters {
+		contents := fmt.Sprintf(`
+package %s
+
+x: 1
+`, string(c))
+		err := os.WriteFile(filepath.Join(testDir, string(c)+".cue"), []byte(contents), 0o644)
+		qt.Assert(t, qt.IsNil(err))
+	}
+
 	insts := Instances([]string{"."}, &Config{
 		Package: "*",
-		Dir:     testDataDir,
+		Dir:     testDir,
 	})
 
 	var actualFiles = []string{}
 	for _, inst := range insts {
 		for _, f := range inst.BuildFiles {
-			if strings.Contains(f.Filename, testDataDir) {
+			if strings.Contains(f.Filename, testDir) {
 				actualFiles = append(actualFiles, filepath.Base(f.Filename))
 			}
 		}
 	}
 	var expectedFiles []string
-	for _, c := range "abcdefghij" {
+	for _, c := range letters {
 		expectedFiles = append(expectedFiles, string(c)+".cue")
 	}
 	qt.Assert(t, qt.DeepEquals(actualFiles, expectedFiles))