docs: add **Debugging ts-jest** section (#2277)

Author: ahnpnl

website/docs/babel7-or-ts.md

@@ -1,4 +1,5 @@
 ---
+id: babel7-or-ts
 title: Babel7 or TypeScript
 ---
 

website/docs/debugging.md

@@ -0,0 +1,22 @@
+---
+id: debugging
+title: Debugging ts-jest
+---
+
+You can activate the debug logger by setting the environment variable `TS_JEST_LOG` before running tests.
+The output of the logger will be in **ts-jest.log** in current working directory.
+
+The debug logger contains some useful information about how internal `ts-jest` works, including which files are processed,
+which Jest config or TypeScript config is used etc.
+
+**Linux/MacOS**
+
+```
+export TS_JEST_LOG=ts-jest.log
+```
+
+**Windows**
+
+```
+set TS_JEST_LOG=ts-jest.log
+```

website/docs/e2e-testing.md

@@ -1,4 +1,5 @@
 ---
+id: e2e-testing
 title: E2E tests flow
 ---
 

website/docs/esm-support.md

@@ -1,4 +1,5 @@
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+id: esm-support
 title: ESM Support
 ---
 

website/docs/installation.md

@@ -1,4 +1,5 @@
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+id: installation
 title: Installation
 ---
 

website/docs/processing.md

@@ -1,4 +1,5 @@
 ---
+id: processing
 title: Jest flow
 ---
 

website/docs/react-native.md

@@ -1,4 +1,5 @@
 ---
+id: react-native
 title: Using with React Native
 ---
 

website/docs/test-helpers.md

@@ -1,4 +1,5 @@
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+id: test-helpers
 title: Test helpers
 ---
 

website/sidebars.js

@@ -22,6 +22,10 @@ module.exports = {
       type: 'doc',
       id: 'migration',
     },
+    {
+      type: 'doc',
+      id: 'debugging',
+    },
     {
       type: 'category',
       label: 'How it works',