Removing ERROR codes present in test files

[Vishalk91-4]

1. Does this PR affect any open issues?(Y/N) and add issue references (e.g. "fix #123", "re #123".):

• N
• Y

2. What is the scope of this PR (e.g. component or file name):

• grammar.js
• expr.txt
• schema.txt
• type.txt

3. Provide a description of the PR(e.g. more details, effects, motivations or doc link):

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Other

4. Are there any breaking changes?(Y/N) and describe the breaking changes(e.g. more details, motivations or doc link):

• N
• Y

5. Are there test cases for these changes?(Y/N) select and add more details, references or doc links:

• Unit test
• Integration test
• Benchmark (add benchmark stats below)
• Manual test (add detailed scripts or steps below)
• Other

[Vishalk91-4]

@Peefy
I'm working on this PR for cleaning up the code of test files
There are still ERROR codes in 4 or so other test cases,
I'll solve them completely then open this PR up, if it's fine with you

[Vishalk91-4]

@Peefy,
I saw some of the ERROR codes already being implemented from the previous PR merged
So, I have fixed the only one remaining
Union Type