Define Unit Tests for Models

[chill5018]

Use #15 to define models for TDD

[chill5018]

Equivalance Testing
ID's: Test that ID's are integers, not double, not string.
Strings: Test that string fields are not numbers 1234!Norway
Price: Should be double, not strings, long, integers, should be greater than 0
Airport Codes: 3 characters, String, not numbers, not contain numbers,
Flight Number: String + Numbers Usually 2 Letters followed by 3-5 numbers
Timestamps: long, fixed length, valid unix timestamp, i.e. after Jan 1, 1970, Long
Origin + Destination Names: String, no numbers, can contain spaces.