diff --git a/.github/instructions/tests.instructions.md b/.github/instructions/tests.instructions.md
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+---
+applyTo: tests/**/*.py
+---
+
+# Testing Guidelines
+
+- Instead of writing new tests, existing tests should ideally be parametrized using `@pytest.mark.parametrize`
+  unless the parametrization is impractical, e.g. by adding more parameters
+- Tests should not use docstrings unless they are _very_ complex