Generator, simply, this is a function that returns the iterator. It's applicable in case of when you do not need to load all data in memory before processing or in cases when we can not receive all data at once or we generate it on the go. In some languages mainly used special keyword yield what returns some value until the next call of the next value from the iterator.

Let’s create the generator.

def gen(steps):
	for i in range(0, steps):
		yield i * i

The yield will generate something like this
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When the creators of golang were developing the architecture of the language they were caring out about developers which will use it in real work. One of the most important processes of development it's the testing, and they did it very convenient and easy to use as they use it themselves.

To create the test enough to declare ".go" file with "_test" postfix in the name. This file will be ignored by the compiler when you will assemble your application. When you run the test every module in the project «go» compile the module with "_test.go" files as independent application and run the test cases one by one.

Let's make simple GO test

First of all, we need what exactly will be to test.

// fact.go
package fact

func Fact(v int) int {
	switch {
	case v < 2:
		return 1
	case v == 2:
		return 2
	}
	return v * Fact(v-1)
}

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