Using Begin to return to a previously defined context

Question

I am trying to understand how contexts in Mathematica work. Suppose I want to write a block of code in which all newly defined symbols are in a particular context.

If I input the following code

Begin["test`"];
Context[]
a=2;
a
End[];
Context[]
a

then I get output

test`a
2
Global`
a

as I would expect. I can also type

test`a

which outputs

2

But what I don't understand is why next inputting

Begin["test`"];
Context[]
a

produces output

test`
a

The Begin["test`"]; line has shifted the context back to test`, so why does inputting a produce output a and not output 2?

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Edit: I don't understand why this is a duplicate of Result about Context is inconsistent with the description of “Power Programming with Mathematica”. In that question, the symbol is assigned a value in both the local and global context. In my example I only assign a value to a in the test context.