feat: add tests for binary search trees

[ridge-kimani]

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Describe your change:

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Documentation change?
• Update tests

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• All new JavaScript files are placed inside an existing directory.
• All filenames should use the UpperCamelCase (PascalCase) style. There should be no spaces in filenames.
  Example:UserProfile.js is allowed but userprofile.js,Userprofile.js,user-Profile.js,userProfile.js are not
• All new algorithms have a URL in their comments that points to Wikipedia or another similar explanation.
• If this pull request resolves one or more open issues then the commit message contains Fixes: #{$ISSUE_NO}.

[anandfresh]

Just a shorthand recommendation.
Checking for if(found) { will check for not null and not undefined .
So no need to explicitly use if (found !== null) {

[ridge-kimani]

The search return value can only be null or a Node, hence the implicit check.

search(val){if(this.value===val){returnthis}elseif(val<this.value&&this.left!==null){returnthis.left.search(val)}elseif(val>this.value&&this.right!==null){returnthis.right.search(val)}returnnull}