Update Testing Approaches readme (#2539)

content/roadmaps/113-qa/content/100-qa-basics/102-testing-approaches/readme.md

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-# Testing approaches
+# Testing Approaches
+
+Test approach has two techniques:
+Proactive - An approach in which the test design process is initiated as early as possible in order to find and fix the defects before the build is created.
+Reactive - An approach in which the testing is not started until after design and coding are completed.
+
+Three approaches are commonly used to implement functional testing:
+- Black Box Testing
+- White Box Testing
+- Gray Box Testing
+
+<ResourceGroupTitle>Free Content</ResourceGroupTitle>
+<BadgeLink colorScheme='yellow' badgeText='Read' href='https://www.qualitylogic.com/knowledge-center/functional-testing-approaches-agile-considerations/'>Functional Testing Approaches and Agile Considerations</BadgeLink>