Junit 5 assertions assertnotnull method

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junit 5 `assertnotnull()`: a deep dive with examples

the `assertnotnull()` method in junit 5 (specifically, in the `org.junit.jupiter.api.assertions` class) is a crucial tool for writing effective and reliable unit tests. it's used to verify that a given object or value is *not* `null`. this is often a preliminary check before performing further operations or assertions on the object. if the object *is* `null`, the assertion will fail, halting the test and indicating a potential problem in the code being tested.

this comprehensive tutorial will explore `assertnotnull()` in detail, covering its syntax, usage scenarios, overloads, custom error messages, and best practices. we'll also compare it to related assertions and discuss common pitfalls.

**1. understanding `assertnotnull()`**

* **purpose:** the primary goal of `assertnotnull()` is to ensure that a variable or expression evaluates to a non-null value. this is fundamental in preventing `nullpointerexception`s, which are notorious for causing application crashes.

* **behavior:**
* if the provided object is `null`, the `assertnotnull()` method throws an `assertionfailederror`, signaling that the test has failed.
* if the provided object is *not* `null`, the assertion passes, and the test execution continues normally.

* **return value:** `assertnotnull()` doesn't return any value. its effect is entirely based on whether it throws an exception or not.

**2. syntax and overloads**

junit 5 provides several overloaded versions of `assertnotnull()`, offering flexibility in how you express your assertion and provide feedback upon failure. the core method signatures are:
let's break down each overload:

* **`assertnotnull(object actual)`:**

- **`actual`:** the object you want to check for nullity.
- this is the simplest form. if `actual` is `null`, the assertion fails with a default error message like: `"expected: not null"`

**example:**



* **`assertnotnull(object actual, string ...

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