test: improve testing in regards to constants (#51)

The codec `ipfs` and `p2p` both are assigned to `0x01a5`, where `ipfs` is the
deprecated name. Make sure that we resolve to `p2p` if that number is used
as input.

README.md

@@ -41,6 +41,14 @@ const multicodec = require('multicodec')
 
 const prefixedProtobuf = multicodec.addPrefix('protobuf', protobufBuffer)
 // prefixedProtobuf 0x50...
+
+// The multicodec codec values can be accessed directly:
+console.log(multicodec.DAG_CBOR)
+// 113
+
+// To get the string representation of a codec, e.g. for error messages:
+console.log(multicodec.print[113])
+// dag-cbor
 ```
 
 ### API

test/multicodec.spec.js

@@ -49,11 +49,38 @@ describe('multicodec', () => {
   it('returns the codec name from code', () => {
     expect(multicodec.getName(144)).to.eql('eth-block')
     expect(multicodec.getName(112)).to.eql('dag-pb')
+    expect(multicodec.getName(0xb201)).to.eql('blake2b-8')
   })
 
   it('returns the codec number from name', () => {
     expect(multicodec.getNumber('eth-block')).to.eql(144)
     expect(multicodec.getNumber('dag-pb')).to.eql(112)
+    // NOTE vmx 2019-09019: Uncomment once
+    // https://github.com/multiformats/js-multicodec/issues/50 is fixed
+    // expect(multicodec.getNumber('blake2b-8')).to.eql(0xb201)
+  })
+
+  it('returns the codec number from constant', () => {
+    expect(multicodec.ETH_BLOCK).to.eql(144)
+    expect(multicodec.DAG_PB).to.eql(112)
+    expect(multicodec.BLAKE2B_8).to.eql(0xb201)
+  })
+
+  it('returns the name from codec number', () => {
+    expect(multicodec.print[144]).to.eql('eth-block')
+    expect(multicodec.print[112]).to.eql('dag-pb')
+    expect(multicodec.print[0x0111]).to.eql('udp')
+    expect(multicodec.print[0xb201]).to.eql('blake2b-8')
+
+    expect(multicodec.print[multicodec.ETH_BLOCK]).to.eql('eth-block')
+    expect(multicodec.print[multicodec.DAG_PB]).to.eql('dag-pb')
+    expect(multicodec.print[multicodec.UDP]).to.eql('udp')
+    expect(multicodec.print[multicodec.BLAKE2B_8]).to.eql('blake2b-8')
+  })
+
+  it('returns p2p when 0x01a5 is used', () => {
+    // `ipfs` and `p2p` are assigned to `0x01a5`, `ipfs` is deprecated
+    expect(multicodec.print[0x01a5]).to.eql('p2p')
   })
 
   it('throws error on unknown codec name when getting the code', () => {