Add unit tests for core components

Cargo.toml

@@ -5,6 +5,14 @@ edition = "2021"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
+[[bin]]
+name = "shift_tool"
+path = "src/main.rs"
+
+[lib]
+name = "vpc_shift_tool"
+path = "src/lib.rs"
+
 [dependencies]
 clap = { version = "4.5.4", features = ["derive"] }
 eframe = "0.30.0"
@@ -21,3 +29,6 @@ chrono = "0.4.40"
 logging = []
 
 default = ["logging"]
+
+[dev-dependencies]
+mock-it = "0.9.0"