docs: Document '%' in expectedJSON case (#28)

Author: kinbiko

README.md

@@ -18,20 +18,24 @@ Create a new `*jsonassert.Asserter` in your test and use this to make assertions
 func TestWhatever(t *testing.T) {
     ja := jsonassert.New(t)
     // find some sort of payload
+    name := "River Tam"
+    age := 16
     ja.Assertf(payload, `
     {
         "name": "%s",
         "age": %d,
+        "averageTestScore": "%s",
         "skills": [
             { "name": "martial arts", "level": 99 },
             { "name": "intelligence", "level": 100 },
             { "name": "mental fortitude", "level": 4 }
         ]
-    }`, "River Tam", 16)
+    }`, name, age, "99%")
 }
 ```
 
 You may pass in `fmt.Sprintf` arguments after the expected JSON structure.
+This feature may be useful for the case when you already have variables in your test with the expected data or when your expected JSON contains a `%` character which could be misinterpreted as a format directive.
 
 `ja.Assertf()` supports assertions against **strings only**.
 

examples_test.go

@@ -25,12 +25,13 @@ func ExampleNew() {
 
 func ExampleAsserter_Assertf_formatArguments() {
 	ja := jsonassert.New(t)
-	ja.Assertf(`{"hello":"世界"}`, `
-		{
-			"hello": "%s"
-		}`, "world")
+	expTestScore := "28%"
+	ja.Assertf(
+		`{ "name": "Jayne Cobb", "age": 36, "averageTestScore": "88%" }`,
+		`{ "name": "Jayne Cobb", "age": 36, "averageTestScore": "%s" }`, expTestScore,
+	)
 	//output:
-	//expected string at '$.hello' to be 'world' but was '世界'
+	//expected string at '$.averageTestScore' to be '28%' but was '88%'
 }
 
 func ExampleAsserter_Assertf_presenceOnly() {

exports.go

@@ -91,6 +91,12 @@ along with the "world" format argument. For example:
 
 	ja.Assertf(`{"hello": "world"}`, `{"hello":"%s"}`, "world")
 
+You may also use format arguments in the case when your expected JSON contains
+a percent character, which would otherwise be interpreted as a
+format-directive.
+
+	ja.Assertf(`{"averageTestScore": "99%"}`, `{"averageTestScore":"%s"}`, "99%")
+
 Additionally, you may wish to make assertions against the *presence* of a
 value, but not against its value. For example: