fix: testing-isolation do not force run all if no packages were found (#3939)

* fix: testing-isolation do not force run all if no packages were found

* add test case

---------

Co-authored-by: Jennifer Davis <[email protected]>

Author: davidcavazos

.github/cloud-samples-tools/pkg/config/config.go

@@ -177,10 +177,6 @@ func (c *Config) Changed(log io.Writer, diffs []string) []string {
 		changedUnique[pkg] = true
 	}
 
-	if len(changedUnique) == 0 {
-		return []string{"."}
-	}
-
 	changed := make([]string, 0, len(changedUnique))
 	for pkg := range changedUnique {
 		if slices.Contains(c.ExcludePackages, pkg) {

.github/cloud-samples-tools/pkg/config/config_test.go

@@ -169,6 +169,7 @@ func TestChanged(t *testing.T) {
 	config := c.Config{
 		PackageFile:     []string{"package.json"},
 		Match:           []string{"*"},
+		Ignore:          []string{"ignored.txt"},
 		ExcludePackages: []string{filepath.Join("testdata", "excluded")},
 	}
 
@@ -180,6 +181,10 @@ func TestChanged(t *testing.T) {
 			diffs:    []string{filepath.Join("testdata", "file.txt")},
 			expected: []string{"."},
 		},
+		{ // Ignored files should not trigger tests.
+			diffs:    []string{filepath.Join("testdata", "ignored.txt")},
+			expected: []string{},
+		},
 		{ // Single affected package.
 			diffs:    []string{filepath.Join("testdata", "my-package", "file.txt")},
 			expected: []string{filepath.Join("testdata", "my-package")},