Traffic light simulation

Requirements

Simulate a set of traffic lights (N, S), (E, W) at an intersection. Prior to switching to the red light, yellow must be displayed for 30 seconds. Lights change every 5 minutes.

Assumptions

• Simulation runs in real-time and outputs at duration intervals
• (N, S) and (E, W) receptively share the same states
• Currently the simulator is started with (N, S) being green and (E, W) red

Notes

• I followed a TDD approach and drove out my solution using IntersectionTest, after having all the cases I was able to re-factor/re-structure with confidence
• I tried to keep my tests lightweight as possible with as little mock/fake as possible
• I wrote a simple system/integration UI test after test driving the intersection unit/package. It requires a sleep but that was the only way I can easily system test it, unit tests take care of using fake schedulers.
• I decided to pass in red/green durations instead of using an enum to allow system testing with different values
• Intersection is currently used to control most of the simulation at this time which I felt allows more flexibility than having lights control state changes.

Setup

This project required Java 8 with gradle 3.3 used to build/test.

• ./gradlew clean build Clean build and run tests
• ./gradlew test Run tests
• ./gradlew run Start simulation which outputs to the terminal

Output 1

Date        Time      North   South   East    West   
2017-08-17  08:04:23  GREEN   GREEN   RED     RED    
2017-08-17  08:08:53  YELLOW  YELLOW  RED     RED    
2017-08-17  08:09:23  RED     RED     GREEN   GREEN  
2017-08-17  08:13:53  RED     RED     YELLOW  YELLOW 
2017-08-17  08:14:23  GREEN   GREEN   RED     RED    
2017-08-17  08:18:53  YELLOW  YELLOW  RED     RED    
2017-08-17  08:19:23  RED     RED     GREEN   GREEN  
2017-08-17  08:23:53  RED     RED     YELLOW  YELLOW 
2017-08-17  08:24:23  GREEN   GREEN   RED     RED    
2017-08-17  08:28:53  YELLOW  YELLOW  RED     RED    
2017-08-17  08:29:23  RED     RED     GREEN   GREEN  
2017-08-17  08:33:53  RED     RED     YELLOW  YELLOW

Output 2

Date        Time      North   South   East    West   
2017-08-17  09:41:01  GREEN   GREEN   RED     RED    
2017-08-17  09:45:31  YELLOW  YELLOW  RED     RED    
2017-08-17  09:46:01  RED     RED     GREEN   GREEN  
2017-08-17  09:50:31  RED     RED     YELLOW  YELLOW 
2017-08-17  09:51:01  GREEN   GREEN   RED     RED    
2017-08-17  09:55:31  YELLOW  YELLOW  RED     RED    
2017-08-17  09:56:01  RED     RED     GREEN   GREEN  
2017-08-17  10:00:31  RED     RED     YELLOW  YELLOW 
2017-08-17  10:01:01  GREEN   GREEN   RED     RED    
2017-08-17  10:05:31  YELLOW  YELLOW  RED     RED    
2017-08-17  10:06:01  RED     RED     GREEN   GREEN  
2017-08-17  10:10:31  RED     RED     YELLOW  YELLOW