test: improve lib/internal/source_map/source_map.js coverage

PR-URL: #42771
Refs: https://coverage.nodejs.org/coverage-0699150267c08fb2/lib/internal/source_map/source_map.js.html#L154
Refs: https://coverage.nodejs.org/coverage-0699150267c08fb2/lib/internal/source_map/source_map.js.html#L165
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Kohei Ueno <kohei.ueno119@gmail.com>

test/fixtures/source-map/disk-index.map

@@ -0,0 +1,30 @@
+{
+  "version": 3,
+  "sources": [
+    "disk.js"
+  ],
+  "sections": [
+    { "offset": {"line": 0, "column": 0 }, "map": 
+     {
+      "version": 3,
+      "sources": [
+        "section.js"
+      ],
+      "names": [
+        "Foo",
+        "[object Object]",
+        "x",
+        "this",
+        "console",
+        "info",
+        "methodC",
+        "a",
+        "b",
+        "methodA"
+      ],
+      "mappings": "MAAMA,IACJC,YAAaC,EAAE,IACbC,KAAKD,EAAIA,EAAIA,EAAI,GACjB,GAAIC,KAAKD,EAAG,CACVE,QAAQC,KAAK,eACR,CACLD,QAAQC,KAAK,aAEfF,KAAKG,UAEPL,UACEG,QAAQC,KAAK,WAEfJ,UACEG,QAAQC,KAAK,aAEfJ,UACEG,QAAQC,KAAK,WAEfJ,UACEG,QAAQC,KAAK,cAIjB,MAAME,EAAI,IAAIP,IAAI,GAClB,MAAMQ,EAAI,IAAIR,IAAI,IAClBO,EAAEE",
+      "sourceRoot": "./"
+     }
+    }
+  ]
+}

test/parallel/test-source-map-api.js

@@ -126,6 +126,27 @@ const { readFileSync } = require('fs');
   assert.strictEqual(Object.keys(result).length, 0);
 }
 
+// SourceMap can be instantiated with Index Source Map V3 object as payload.
+{
+  const payload = JSON.parse(readFileSync(
+    require.resolve('../fixtures/source-map/disk-index.map'), 'utf8'
+  ));
+  const sourceMap = new SourceMap(payload);
+  const {
+    originalLine,
+    originalColumn,
+    originalSource
+  } = sourceMap.findEntry(0, 29);
+  assert.strictEqual(originalLine, 2);
+  assert.strictEqual(originalColumn, 4);
+  assert(originalSource.endsWith('section.js'));
+  // The stored payload should be a clone:
+  assert.strictEqual(payload.mappings, sourceMap.payload.mappings);
+  assert.notStrictEqual(payload, sourceMap.payload);
+  assert.strictEqual(payload.sources[0], sourceMap.payload.sources[0]);
+  assert.notStrictEqual(payload.sources, sourceMap.payload.sources);
+}
+
 // Test various known decodings to ensure decodeVLQ works correctly.
 {
   function makeMinimalMap(column) {