Add some unit tests for extension detection

src/ShellCheck/Analytics.hs

@@ -484,7 +484,7 @@ checkShebang params (T_Annotation _ list t) =
 checkShebang params (T_Script id sb _) = execWriter $ do
     unless (shellTypeSpecified params) $ do
         when (sb == "") $
-            err id 2148 "Tips depend on target shell and yours is unknown. Add a shebang or a .bash, .ksh, .dash extension to the filename."
+            err id 2148 "Tips depend on target shell and yours is unknown. Add a shebang."
         when (executableFromShebang sb == "ash") $
             warn id 2187 "Ash scripts will be checked as Dash. Add '# shellcheck shell=dash' to silence."
     unless (null sb) $ do

src/ShellCheck/Checker.hs

@@ -244,5 +244,35 @@ prop_sourcePartOfOriginalScript = -- #1181: -x disabled posix warning for 'sourc
 
 prop_spinBug1413 = null $ check "fun() {\n# shellcheck disable=SC2188\n> /dev/null\n}\n"
 
+prop_deducesTypeFromExtension = null result
+  where
+    result = checkWithSpec [] emptyCheckSpec {
+        csFilename = "file.ksh",
+        csScript = "(( 3.14 ))"
+    }
+
+prop_deducesTypeFromExtension2 = result == [2079]
+  where
+    result = checkWithSpec [] emptyCheckSpec {
+        csFilename = "file.bash",
+        csScript = "(( 3.14 ))"
+    }
+
+prop_shExtensionDoesntMatter = result == [2148]
+  where
+    result = checkWithSpec [] emptyCheckSpec {
+        csFilename = "file.sh",
+        csScript = "echo 'hello world'"
+    }
+
+prop_sourcedFileUsesOriginalShellExtension = result == [2079]
+  where
+    result = checkWithSpec [("file.ksh", "(( 3.14 ))")] emptyCheckSpec {
+        csFilename = "file.bash",
+        csScript = "source file.ksh",
+        csCheckSourced = True
+    }
+
+
 return []
 runTests = $quickCheckAll