Parses strategy correctly (+ tests).

Fixes #22

__fixtures__/yarn.lock

@@ -2,10 +2,14 @@
 # yarn lockfile v1
 
 
-lodash@>=1.0.0:
-  version "1.3.1"
-  resolved "https://registry.yarnpkg.com/lodash/-/lodash-1.3.1.tgz#a4663b53686b895ff074e2ba504dfb76a8e2b770"
+library@>=1.0.0, library@>=1.1.0:
+  version "3.0.0"
+  resolved "https://example.net/library@^3.0.0"
 
-lodash@>=2.0.0:
+library@^2.0.0:
+  version "2.1.0"
+  resolved "https://example.net/library@^2.1.0"
+
+lodash@>=1.0.0, lodash@>=2.0.0:
   version "4.17.4"
   resolved "https://registry.yarnpkg.com/lodash/-/lodash-4.17.4.tgz#78203a4d1c328ae1d86dca6460e369b57f4055ae"

__tests__/cli.js

@@ -92,3 +92,17 @@ test('line endings are retained', async () => {
         await writeFile(yarnLockFilePath, oldFileContent, 'utf8');
     }
 });
+
+test.only('uses fewer strategy', async () => {
+    const { stdout, stderr } = await execFile(process.execPath, [
+        cliFilePath,
+        '--print',
+        '-s',
+        'fewer',
+        yarnLockFilePath,
+    ]);
+    expect(stdout).not.toContain('library@>=1.0.0:');
+    expect(stdout).toContain('library@>=1.0.0, library@>=1.1.0, library@^2.0.0:');
+    expect(stdout).toContain('resolved "https://example.net/library@^2.1.0"');
+    expect(stderr).toBe('');
+});

cli.js

@@ -12,7 +12,6 @@ commander
     .option(
         '-s, --strategy <strategy>',
         'deduplication strategy. Valid values: fewer, highest. Default is "highest"',
-        /^(fewer|highest)$/i,
         'highest'
     )
     .option('-l, --list', 'do not change yarn.lock, just output the diagnosis')
@@ -24,20 +23,25 @@ commander
     .option('--print', 'instead of saving the deduplicated yarn.lock, print the result in stdout');
 commander.parse(process.argv);
 if (!commander.args.length) commander.help();
+if (commander.strategy !== 'highest' && commander.strategy !== 'fewer') {
+    console.error(`Invalid strategy ${commander.strategy}`);
+    commander.help();
+}
 
 const file = commander.args[0];
 
 try {
     const yarnLock = fs.readFileSync(file, 'utf8');
+    const useMostCommon = commander.strategy === 'fewer';
 
     if (commander.list) {
         listDuplicates(yarnLock, {
-            useMostCommon: commander.mostCommon,
+            useMostCommon,
             includePackages: commander.packages,
         }).forEach(logLine => console.log(logLine));
     } else {
         let dedupedYarnLock = fixDuplicates(yarnLock, {
-            useMostCommon: commander.mostCommon,
+            useMostCommon,
             includePackages: commander.packages,
         });