update project structure

src/tests/assertions.md

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+# Assertions

src/tests/benchmark.md

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+# Benchmark
+
+https://doc.rust-lang.org/unstable-book/library-features/test.html

src/tests/intro.md

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+# Tests

src/tests/unit-integration.md

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+# Unit and Integration

src/tests/write-tests.md

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+# Write Tests