add spec for spirit core

spec/spirit-spec.js

@@ -0,0 +1,85 @@
+const spirit = require("../index")
+
+describe("spirit spec", () => {
+
+  it("it wraps a handler and middlewares into a reducer function which reduces through the middlewares and handler and 'rewinds' flowing backwards returning the result; the order -> last middleware is the first input, last output. the first middleware is the last input, first output", (done) => {
+    const handler = (input) => {
+      expect(input).toBe("abc")
+      return "out"
+    }
+
+    const middlewares = [
+      (handler) => {
+        return (input) => {
+          input += "c"
+          return handler(input).then((result) => {
+            return result + "1"
+          })
+        }
+      },
+      (handler) => {
+        return (input) => {
+          input += "b"
+          return handler(input).then((result) => {
+            return result + "2"
+          })
+        }
+      }
+    ]
+
+    const reducer = spirit.core(handler, middlewares)
+    reducer("a").then((result) => {
+      expect(result).toBe("out12")
+      done()
+    })
+  })
+
+  it("middlewares can decide to stop passing data forward (input), data 'rewinds' and flows back out through all middleware called along the way", () => {
+    const handler = (input) => {
+      throw "never gets run"
+    }
+    const middlewares = [
+      (handler) => {
+        return (input) => {
+          expect(input).toBe("ab")
+          return Promise.resolve("stop")
+        }
+      },
+      (handler) => {
+        return (input) => {
+          input += "b"
+          return handler(input).then((result) => {
+            return result + "2"
+          })
+        }
+      }
+    ]
+    const reducer = spirit.core(handler, middlewares)
+    reducer("a").then((result) => {
+      expect(result).toBe("stop2")
+      done()
+    })
+  })
+
+  it("a adapter transforms data between spirit and another interface. an adapter controls the first entry point and last exit point, it can also catch any uncaught errors along the way", () => {
+    const handler = (input) => {
+      throw "catch"
+    }
+
+    const middlewares = [
+      (handler) => {
+        return (input) => {
+          return handler(input)
+        }
+      }
+    ]
+
+    const reducer = spirit.core(handler, middlewares)
+    const adapter = () => {
+      reducer("hi").catch((err) => {
+        expect(err).toBe("catch")
+      })
+    }
+  })
+
+})