Fix branch name symmetry issue for Amplify

.changelog/20426.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+aws/resource_aws_amplify_branch: Correctly handle branch names that contain '/'
+```

aws/internal/service/amplify/id.go

@@ -34,7 +34,7 @@ func BranchCreateResourceID(appID, branchName string) string {
 }
 
 func BranchParseResourceID(id string) (string, string, error) {
-	parts := strings.Split(id, branchResourceIDSeparator)
+	parts := strings.SplitN(id, branchResourceIDSeparator, 2)
 
 	if len(parts) == 2 && parts[0] != "" && parts[1] != "" {
 		return parts[0], parts[1], nil

aws/internal/service/amplify/id_test.go

@@ -0,0 +1,68 @@
+package amplify_test
+
+import (
+	"testing"
+
+	tfamplify "github.com/terraform-providers/terraform-provider-aws/aws/internal/service/amplify"
+)
+
+func TestBranchParseResourceID(t *testing.T) {
+	testCases := []struct {
+		TestName           string
+		InputID            string
+		ExpectError        bool
+		ExpectedAppID      string
+		ExpectedBranchName string
+	}{
+		{
+			TestName:    "empty ID",
+			InputID:     "",
+			ExpectError: true,
+		},
+		{
+			TestName:    "incorrect format",
+			InputID:     "test",
+			ExpectError: true,
+		},
+		{
+			TestName:           "valid ID",
+			InputID:            tfamplify.BranchCreateResourceID("appID", "branchName"),
+			ExpectedAppID:      "appID",
+			ExpectedBranchName: "branchName",
+		},
+		{
+			TestName:           "valid ID one slash",
+			InputID:            tfamplify.BranchCreateResourceID("appID", "part1/part_2"),
+			ExpectedAppID:      "appID",
+			ExpectedBranchName: "part1/part_2",
+		},
+		{
+			TestName:           "valid ID three slashes",
+			InputID:            tfamplify.BranchCreateResourceID("appID", "part1/part_2/part-3/part4"),
+			ExpectedAppID:      "appID",
+			ExpectedBranchName: "part1/part_2/part-3/part4",
+		},
+	}
+
+	for _, testCase := range testCases {
+		t.Run(testCase.TestName, func(t *testing.T) {
+			gotAppID, gotBranchName, err := tfamplify.BranchParseResourceID(testCase.InputID)
+
+			if err == nil && testCase.ExpectError {
+				t.Fatalf("expected error")
+			}
+
+			if err != nil && !testCase.ExpectError {
+				t.Fatalf("unexpected error")
+			}
+
+			if gotAppID != testCase.ExpectedAppID {
+				t.Errorf("got AppID %s, expected %s", gotAppID, testCase.ExpectedAppID)
+			}
+
+			if gotBranchName != testCase.ExpectedBranchName {
+				t.Errorf("got BranchName %s, expected %s", gotBranchName, testCase.ExpectedBranchName)
+			}
+		})
+	}
+}