lukas-krecan#567 Ease assertions on content of JSON files

json-unit-assertj/src/main/java/net/javacrumbs/jsonunit/assertj/JsonFileAssert.java

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+package net.javacrumbs.jsonunit.assertj;
+
+import net.javacrumbs.jsonunit.assertj.JsonAssert.ConfigurableJsonAssert;
+import org.assertj.core.api.AbstractFileAssert;
+import org.assertj.core.internal.Files;
+import org.jetbrains.annotations.NotNull;
+
+import java.io.File;
+import java.io.IOException;
+import java.io.UncheckedIOException;
+import java.nio.charset.Charset;
+
+import static java.nio.file.Files.readAllBytes;
+import static net.javacrumbs.jsonunit.assertj.JsonAssertions.assertThatJson;
+import static org.assertj.core.internal.Files.instance;
+
+/**
+ * Wrapper on {@link ConfigurableJsonAssert} to retrieve JSON from a file.
+ */
+public class JsonFileAssert extends AbstractFileAssert<JsonFileAssert> {
+    private final Files files = instance();
+
+    /**
+     * Assert json properties in a file from its path.
+     *
+     * <pre>{@code
+     * assertThatJsonFile("path/to/file.json").isFile()
+     *     .hasContent().inPath("test1").isEqualTo(2);
+     * }</pre>
+     */
+    @NotNull
+    public static JsonFileAssert assertThatJsonFile(@NotNull String path) {
+        return new JsonFileAssert(new File(path));
+    }
+
+    /**
+     * Assert json properties in a file.
+     *
+     * <pre>{@code
+     * assertThatJsonFile(jsonFile).isFile()
+     *     .hasContent().inPath("test1").isEqualTo(2);
+     * }</pre>
+     */
+    @NotNull
+    public static JsonFileAssert assertThatJsonFile(@NotNull File file) {
+        return new JsonFileAssert(file);
+    }
+
+    private JsonFileAssert(File actual) {
+        super(actual, JsonFileAssert.class);
+    }
+
+    /**
+     * Convert file content to assertable JSON.
+     *
+     * @return ConfigurableJsonAssert to perform assertions on json content
+     * @throws IllegalArgumentException when file content is not valid JSON
+     */
+    public ConfigurableJsonAssert hasContent() {
+        return hasContent(Charset.defaultCharset());
+    }
+
+    /**
+     * Convert file content to assertable JSON with provided charset.
+     *
+     * @param charset The charset of the JSON file
+     * @return ConfigurableJsonAssert to perform assertions on json content
+     * @throws IllegalArgumentException when file content is not valid JSON
+     */
+    public ConfigurableJsonAssert hasContent(Charset charset) {
+        files.assertCanRead(info, actual);
+        return assertThatJson(readFile(charset));
+    }
+
+    private String readFile(Charset charset) {
+        try {
+            return new String(readAllBytes(actual.toPath()), charset);
+        } catch (IOException e) {
+            throw new UncheckedIOException(String.format("Failed to read %s content with %s charset", actual, charset), e);
+        }
+    }
+}

json-unit-assertj/src/test/kotlin/net/javacrumbs/jsonunit/assertj/JsonFileAssertTest.kt

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+package net.javacrumbs.jsonunit.assertj
+
+import net.javacrumbs.jsonunit.assertj.JsonFileAssert.assertThatJsonFile
+import org.assertj.core.api.Assertions.assertThatThrownBy
+import org.junit.jupiter.api.Test
+import java.io.File
+import java.nio.charset.Charset
+
+class JsonFileAssertTest {
+
+    @Test
+    fun `assertJsonFile should allow JSON assertions on JSON file when path is provided`() {
+        assertThatJsonFile("src/test/resources/test.json")
+                .hasContent().node("key").isEqualTo("value")
+    }
+
+    @Test
+    fun `assertJsonFile should allow JSON assertions on JSON file when file is provided`() {
+        assertThatJsonFile(File("src/test/resources/test.json"))
+                .hasContent().node("key").isEqualTo("value")
+    }
+
+    @Test
+    fun `assertJsonFile should allow defining charset for the JSON file`() {
+        assertThatJsonFile(File("src/test/resources/test.json"))
+                .hasContent(Charset.forName("UTF-8")).node("key").isEqualTo("value")
+    }
+
+    @Test
+    fun `assertJsonFile should throw an IllegalArgumentException when JSON file is invalid`() {
+        assertThatThrownBy {
+            assertThatJsonFile("src/test/resources/invalid.json").hasContent()
+        }.isInstanceOf(IllegalArgumentException::class.java)
+    }
+
+    @Test
+    fun `assertJsonFile should throw an AssertionError when JSON file is not found`() {
+        assertThatThrownBy {
+            assertThatJsonFile("src/test/resources/not_found.json").hasContent()
+        }.isInstanceOf(AssertionError::class.java)
+    }
+}

json-unit-assertj/src/test/resources/invalid.json

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+{
+  "key":

json-unit-assertj/src/test/resources/test.json

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+{
+  "key": "value"
+}