Add smart contract for checking passport status (#72)

contracts/INationCred.sol

@@ -8,4 +8,11 @@ interface INationCred {
      * @param passportID The NFT passport ID
      */
     function isActive(uint16 passportID) external view returns (bool);
+
+    /**
+     * Returns `true` if a citizen's vote-escrowed `$NATION` balance has dropped below the passport expiry threshold; `false` otherwise.
+     *
+     * @param citizen The address of the passport owner
+     */
+    function isPassportExpired(address citizen) external view returns (bool);
 }

contracts/NationCred.sol

@@ -33,4 +33,9 @@ contract NationCred is INationCred {
         }
         return false;
     }
+
+    function isPassportExpired(address citizen) public view returns (bool) {
+        // TO DO
+        return true;
+    }
 }

test/NationCred.ts

@@ -68,4 +68,14 @@ describe("NationCred", function () {
     expect(await nationCred.isActive(419)).to.equal(true);
     expect(await nationCred.isActive(420)).to.equal(false);
   });
+
+  it("isPassportExpired - no passport", async function () {
+    const [owner] = await ethers.getSigners();
+
+    const NationCred = await ethers.getContractFactory("NationCred");
+    const nationCred = await NationCred.deploy();
+    await nationCred.deployed();
+
+    expect(await nationCred.isPassportExpired(owner.address)).to.equal(true);
+  });
 });