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DESIGN_PRINCIPLES.md

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+# Design principles
+
+This documents aims to capture the design principles that went into this library.
+It should serve as a reference point when making decisions on what features to include or exclude.
+
+## Simple
+
+One of most important goals that we want to adhere to is creating a _simple_ API.
+Overall, this means keeping the API as small as possible to get the task done.
+When in doubt, we'd rather not add flags or configuration options for certain use cases.
+
+Tests should be easier to write, easy to understand and easy to maintain.
+`testcontainers` aims to support this as much as possible.
+Having too many configuration options makes it harder for users to achieve this goal.
+
+Another advantage of a small, public API is that we have to make fewer breaking changes.
+This makes upgrades easier for our users.
+
+## Reliable
+
+Tests need to be reliable to provide value.
+We strive to make `testcontainers` as reliable as possible and try to control as many aspects of the container to make sure they work consistently.
+
+One consequence of this decision is that the container _tag_ is typically not configurable for images that ship with `testcontainers`.
+Whilst an image behind a tag can also change, image authors tend to preserve compatibility there.
+If we were to allow users to change the `tag` of an image, we wouldn't be able to guarantee that it works because we cannot test all combinations.