test: add cucumber steps for checking JSON reports

Add the following Cucumber steps:

- `Then the JSON report is valid`
- `Then JSON at {string} contains {int} items`
- `Then JSON at {string} has no null values`
- `Then JSON at {string} is not null`
- `Then JSON at {string} is {string}`

JSON values or arrays are inspected using expressions based on a JSON path DSL,
and asserted with the [json-path-assert](https://github.com/json-path/JsonPath) library.

pom.xml

@@ -160,6 +160,11 @@
             <version>1.1.1</version>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>com.jayway.jsonpath</groupId>
+            <artifactId>json-path-assert</artifactId>
+            <version>2.8.0</version>
+        </dependency>
         <dependency>
             <groupId>xmlunit</groupId>
             <artifactId>xmlunit</artifactId>
@@ -190,6 +195,11 @@
             <version>2.1</version>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>org.slf4j</groupId>
+            <artifactId>slf4j-nop</artifactId>
+            <version>1.7.36</version>
+        </dependency>
     </dependencies>
 
     <build>

src/test/java/org/w3c/epubcheck/test/JSONReportAssertionSteps.java

@@ -0,0 +1,54 @@
+package org.w3c.epubcheck.test;
+
+import static com.jayway.jsonpath.matchers.JsonPathMatchers.hasJsonPath;
+import static com.jayway.jsonpath.matchers.JsonPathMatchers.isJson;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.everyItem;
+import static org.hamcrest.Matchers.hasSize;
+import static org.hamcrest.Matchers.not;
+import static org.hamcrest.Matchers.notNullValue;
+import static org.hamcrest.Matchers.nullValue;
+
+import io.cucumber.java.en.Then;
+
+public class JSONReportAssertionSteps
+{
+
+  private TestReport report;
+
+  public JSONReportAssertionSteps(TestConfiguration configuration)
+  {
+    this.report = configuration.getReport();
+  }
+
+  @Then("the JSON report is valid")
+  public void jsonIsValid()
+  {
+    assertThat(report.getOutput(), isJson());
+  }
+
+  @Then("JSON at {string} contains {int} items")
+  public void jsonArrayHasSize(String path, int size)
+  {
+    assertThat(report.getOutput(), hasJsonPath(path, hasSize(size)));
+  }
+
+  @Then("JSON at {string} is {string}")
+  public void jsonValueIs(String path, String value)
+  {
+    assertThat(report.getOutput(), hasJsonPath(path, equalTo(value)));
+  }
+
+  @Then("JSON at {string} is not null")
+  public void jsonValueIsNotNull(String path)
+  {
+    assertThat(report.getOutput(), hasJsonPath(path, not(nullValue())));
+  }
+
+  @Then("JSON at {string} has no null values")
+  public void jsonValuesAreNotNull(String path)
+  {
+    assertThat(report.getOutput(), hasJsonPath(path, everyItem(notNullValue())));
+  }
+}