I2C inout port signal VHDL simulation

Hello there;

I have simulated a module with an external temperature sensor(LM75). In 
the top Level module the port were defined as "inout" type something 
like this

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      i2c_scl    : inout std_logic;

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      i2c_sda    : inout std_logic;

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      ….;

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    achitecture behav of top_level is

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    Signal i2c_scl_int    : std_logic;

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    Signal i2c_sda_int    : std_logic;

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    …. ;

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begin

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    i2c_scl <= '0' when i2c_scl_int ='0' else 'Z';

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    i2c_sda <= '0' when i2c_sda_int ='0' else 'Z';

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    … ;

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end;

With the above Code my Output was "ZZ" every time and I have to modify 
the LM75 source Code as well as the i2c Controller Code to get a proper 
Output Signal.

I would like to know if there is any other Approach by not modifying the 
source Code and only add some Code in the testbench?

Thank you.