Retry: Make ConfiguredJarList immutable

By making the Append and RemoveList methods return a new list instead
of modifying the existing list it makes the ConfiguredJarList usages
easier to reason about and safer to use, especially considering that
they are primarily used in global configuration.

Added some tests for Append/RemoveList to ensure that they work and
do not modify the original or result in newly created lists sharing
storage with the original which would lead to corruption.

Bug: 171756871
Bug: 171479578
Test: m nothing
      EMMA_INSTRUMENT=true EMMA_INSTRUMENT_FRAMEWORK=true m nothing
Change-Id: I541c4686ecdd45c6a0c8b1c93fedf0fcd5952e2b

android/config_test.go

@@ -91,3 +91,49 @@ func TestMissingVendorConfig(t *testing.T) {
 		t.Errorf("Expected false")
 	}
 }
+
+func assertStringEquals(t *testing.T, expected, actual string) {
+	if actual != expected {
+		t.Errorf("expected %q found %q", expected, actual)
+	}
+}
+
+func TestConfiguredJarList(t *testing.T) {
+	list1 := CreateTestConfiguredJarList([]string{"apex1:jarA"})
+
+	t.Run("create", func(t *testing.T) {
+		assertStringEquals(t, "apex1:jarA", list1.String())
+	})
+
+	list2 := list1.Append("apex2", "jarB")
+	t.Run("append", func(t *testing.T) {
+		assertStringEquals(t, "apex1:jarA,apex2:jarB", list2.String())
+	})
+
+	t.Run("append does not modify", func(t *testing.T) {
+		assertStringEquals(t, "apex1:jarA", list1.String())
+	})
+
+	// Make sure that two lists created by appending to the same list do not share storage.
+	list3 := list1.Append("apex3", "jarC")
+	t.Run("append does not share", func(t *testing.T) {
+		assertStringEquals(t, "apex1:jarA,apex2:jarB", list2.String())
+		assertStringEquals(t, "apex1:jarA,apex3:jarC", list3.String())
+	})
+
+	list4 := list3.RemoveList(list1)
+	t.Run("remove", func(t *testing.T) {
+		assertStringEquals(t, "apex3:jarC", list4.String())
+	})
+
+	t.Run("remove does not modify", func(t *testing.T) {
+		assertStringEquals(t, "apex1:jarA,apex3:jarC", list3.String())
+	})
+
+	// Make sure that two lists created by removing from the same list do not share storage.
+	list5 := list3.RemoveList(CreateTestConfiguredJarList([]string{"apex3:jarC"}))
+	t.Run("remove", func(t *testing.T) {
+		assertStringEquals(t, "apex3:jarC", list4.String())
+		assertStringEquals(t, "apex1:jarA", list5.String())
+	})
+}